Add Gregory K. Johnson's revised version of mailbox.py (funded by

the 2005 Summer of Code).

The revision adds a number of new mailbox classes that support adding
and removing messages; these classes also support mailbox locking and
default to using email.Message instead of rfc822.Message.

The old mailbox classes are largely left alone for backward compatibility.
The exception is the Maildir class, which was present in the old module
and now inherits from the new classes.  The Maildir class's interface
is pretty simple, though, so I think it'll be compatible with existing
code.

(The change to the NEWS file also adds a missing word to a different
news item, which unfortunately required rewrapping the line.)

Doc/lib/libmailbox.tex

 \section{\module{mailbox} ---
-         Read various mailbox formats}
+          Manipulate mailboxes in various formats}
 
-\declaremodule{standard}{mailbox}
-\modulesynopsis{Read various mailbox formats.}
+\declaremodule{}{mailbox}
+\moduleauthor{Gregory K.~Johnson}{gkj@gregorykjohnson.com}
+\sectionauthor{Gregory K.~Johnson}{gkj@gregorykjohnson.com}
+\modulesynopsis{Manipulate mailboxes in various formats}
 
 
-This module defines a number of classes that allow easy and uniform
-access to mail messages in a (\UNIX) mailbox.
+This module defines two classes, \class{Mailbox} and \class{Message}, for
+accessing and manipulating on-disk mailboxes and the messages they contain.
+\class{Mailbox} offers a dictionary-like mapping from keys to messages.
+\class{Message} extends the \module{email.Message} module's \class{Message}
+class with format-specific state and behavior. Supported mailbox formats are
+Maildir, mbox, MH, Babyl, and MMDF.
+
+\begin{seealso}
+    \seemodule{email}{Represent and manipulate messages.}
+\end{seealso}
+
+\subsection{\class{Mailbox} objects}
+\label{mailbox-objects}
+
+\begin{classdesc*}{Mailbox}
+A mailbox, which may be inspected and modified.
+\end{classdesc*}
+
+The \class{Mailbox} interface is dictionary-like, with small keys
+corresponding to messages. Keys are issued by the \class{Mailbox} instance
+with which they will be used and are only meaningful to that \class{Mailbox}
+instance. A key continues to identify a message even if the corresponding
+message is modified, such as by replacing it with another message. Messages may
+be added to a \class{Mailbox} instance using the set-like method
+\method{add()} and removed using a \code{del} statement or the set-like methods
+\method{remove()} and \method{discard()}.
+
+\class{Mailbox} interface semantics differ from dictionary semantics in some
+noteworthy ways. Each time a message is requested, a new representation
+(typically a \class{Message} instance) is generated, based upon the current
+state of the mailbox. Similarly, when a message is added to a \class{Mailbox}
+instance, the provided message representation's contents are copied. In neither
+case is a reference to the message representation kept by the \class{Mailbox}
+instance.
+
+The default \class{Mailbox} iterator iterates over message representations, not
+keys as the default dictionary iterator does. Moreover, modification of a
+mailbox during iteration is safe and well-defined. Messages added to the
+mailbox after an iterator is created will not be seen by the iterator. Messages
+removed from the mailbox before the iterator yields them will be silently
+skipped, though using a key from an iterator may result in a
+\exception{KeyError} exception if the corresponding message is subsequently
+removed.
+
+\class{Mailbox} itself is intended to define an interface and to be inherited
+from by format-specific subclasses but is not intended to be instantiated.
+Instead, you should instantiate a subclass.
+
+\class{Mailbox} instances have the following methods:
+
+\begin{methoddesc}{add}{message}
+Add \var{message} to the mailbox and return the key that has been assigned to
+it.
+
+Parameter \var{message} may be a \class{Message} instance, an
+\class{email.Message.Message} instance, a string, or a file-like object (which
+should be open in text mode). If \var{message} is an instance of the
+appropriate format-specific \class{Message} subclass (e.g., if it's an
+\class{mboxMessage} instance and this is an \class{mbox} instance), its
+format-specific information is used. Otherwise, reasonable defaults for
+format-specific information are used.
+\end{methoddesc}
+
+\begin{methoddesc}{remove}{key}
+\methodline{__delitem__}{key}
+\methodline{discard}{key}
+Delete the message corresponding to \var{key} from the mailbox.
+
+If no such message exists, a \exception{KeyError} exception is raised if the
+method was called as \method{remove()} or \method{__delitem__()} but no
+exception is raised if the method was called as \method{discard()}. The
+behavior of \method{discard()} may be preferred if the underlying mailbox
+format supports concurrent modification by other processes.
+\end{methoddesc}
+
+\begin{methoddesc}{__setitem__}{key, message}
+Replace the message corresponding to \var{key} with \var{message}. Raise a
+\exception{KeyError} exception if no message already corresponds to \var{key}.
+
+As with \method{add()}, parameter \var{message} may be a \class{Message}
+instance, an \class{email.Message.Message} instance, a string, or a file-like
+object (which should be open in text mode). If \var{message} is an instance of
+the appropriate format-specific \class{Message} subclass (e.g., if it's an
+\class{mboxMessage} instance and this is an \class{mbox} instance), its
+format-specific information is used. Otherwise, the format-specific information
+of the message that currently corresponds to \var{key} is left unchanged. 
+\end{methoddesc}
+
+\begin{methoddesc}{iterkeys}{}
+\methodline{keys}{}
+Return an iterator over all keys if called as \method{iterkeys()} or return a
+list of keys if called as \method{keys()}.
+\end{methoddesc}
+
+\begin{methoddesc}{itervalues}{}
+\methodline{__iter__}{}
+\methodline{values}{}
+Return an iterator over representations of all messages if called as
+\method{itervalues()} or \method{__iter__()} or return a list of such
+representations if called as \method{values()}. The messages are represented as
+instances of the appropriate format-specific \class{Message} subclass unless a
+custom message factory was specified when the \class{Mailbox} instance was
+initialized. \note{The behavior of \method{__iter__()} is unlike that of
+dictionaries, which iterate over keys.}
+\end{methoddesc}
+
+\begin{methoddesc}{iteritems}{}
+\methodline{items}{}
+Return an iterator over (\var{key}, \var{message}) pairs, where \var{key} is a
+key and \var{message} is a message representation, if called as
+\method{iteritems()} or return a list of such pairs if called as
+\method{items()}. The messages are represented as instances of the appropriate
+format-specific \class{Message} subclass unless a custom message factory was
+specified when the \class{Mailbox} instance was initialized.
+\end{methoddesc}
+
+\begin{methoddesc}{get}{key\optional{, default=None}}
+\methodline{__getitem__}{key}
+Return a representation of the message corresponding to \var{key}. If no such
+message exists, \var{default} is returned if the method was called as
+\method{get()} and a \exception{KeyError} exception is raised if the method was
+called as \method{__getitem__()}. The message is represented as an instance of
+the appropriate format-specific \class{Message} subclass unless a custom
+message factory was specified when the \class{Mailbox} instance was
+initialized.
+\end{methoddesc}
+
+\begin{methoddesc}{get_message}{key}
+Return a representation of the message corresponding to \var{key} as an
+instance of the appropriate format-specific \class{Message} subclass, or raise
+a \exception{KeyError} exception if no such message exists.
+\end{methoddesc}
+
+\begin{methoddesc}{get_string}{key}
+Return a string representation of the message corresponding to \var{key}, or
+raise a \exception{KeyError} exception if no such message exists.
+\end{methoddesc}
+
+\begin{methoddesc}{get_file}{key}
+Return a file-like representation of the message corresponding to \var{key},
+or raise a \exception{KeyError} exception if no such message exists. The
+file-like object behaves as if open in binary mode. This file should be closed
+once it is no longer needed.
+
+\note{Unlike other representations of messages, file-like representations are
+not necessarily independent of the \class{Mailbox} instance that created them
+or of the underlying mailbox. More specific documentation is provided by each
+subclass.}
+\end{methoddesc}
+
+\begin{methoddesc}{has_key}{key}
+\methodline{__contains__}{key}
+Return \code{True} if \var{key} corresponds to a message, \code{False}
+otherwise.
+\end{methoddesc}
+
+\begin{methoddesc}{__len__}{}
+Return a count of messages in the mailbox.
+\end{methoddesc}
+
+\begin{methoddesc}{clear}{}
+Delete all messages from the mailbox.
+\end{methoddesc}
+
+\begin{methoddesc}{pop}{key\optional{, default}}
+Return a representation of the message corresponding to \var{key} and delete
+the message. If no such message exists, return \var{default} if it was supplied
+or else raise a \exception{KeyError} exception. The message is represented as
+an instance of the appropriate format-specific \class{Message} subclass unless
+a custom message factory was specified when the \class{Mailbox} instance was
+initialized.
+\end{methoddesc}
+
+\begin{methoddesc}{popitem}{}
+Return an arbitrary (\var{key}, \var{message}) pair, where \var{key} is a key
+and \var{message} is a message representation, and delete the corresponding
+message. If the mailbox is empty, raise a \exception{KeyError} exception. The
+message is represented as an instance of the appropriate format-specific
+\class{Message} subclass unless a custom message factory was specified when the
+\class{Mailbox} instance was initialized.
+\end{methoddesc}
+
+\begin{methoddesc}{update}{arg}
+Parameter \var{arg} should be a \var{key}-to-\var{message} mapping or an
+iterable of (\var{key}, \var{message}) pairs. Updates the mailbox so that, for
+each given \var{key} and \var{message}, the message corresponding to \var{key}
+is set to \var{message} as if by using \method{__setitem__()}. As with
+\method{__setitem__()}, each \var{key} must already correspond to a message in
+the mailbox or else a \exception{KeyError} exception will be raised, so in
+general it is incorrect for \var{arg} to be a \class{Mailbox} instance.
+\note{Unlike with dictionaries, keyword arguments are not supported.}
+\end{methoddesc}
+
+\begin{methoddesc}{flush}{}
+Write any pending changes to the filesystem. For some \class{Mailbox}
+subclasses, changes are always written immediately and this method does
+nothing.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+Acquire an exclusive advisory lock on the mailbox so that other processes know
+not to modify it. An \exception{ExternalClashError} is raised if the lock is
+not available. The particular locking mechanisms used depend upon the mailbox
+format.
+\end{methoddesc}
+
+\begin{methoddesc}{unlock}{}
+Release the lock on the mailbox, if any.
+\end{methoddesc}
+
+\begin{methoddesc}{close}{}
+Flush the mailbox, unlock it if necessary, and close any open files. For some
+\class{Mailbox} subclasses, this method does nothing.
+\end{methoddesc}
+
+
+\subsubsection{\class{Maildir}}
+\label{mailbox-maildir}
+
+\begin{classdesc}{Maildir}{dirname\optional{, factory=rfc822.Message\optional{,
+create=True}}}
+A subclass of \class{Mailbox} for mailboxes in Maildir format. Parameter
+\var{factory} is a callable object that accepts a file-like message
+representation (which behaves as if open in binary mode) and returns a custom
+representation. If \var{factory} is \code{None}, \class{MaildirMessage} is used
+as the default message representation. If \var{create} is \code{True}, the
+mailbox is created if it does not exist.
+
+It is for historical reasons that \var{factory} defaults to
+\class{rfc822.Message} and that \var{dirname} is named as such rather than
+\var{path}. For a \class{Maildir} instance that behaves like instances of other
+\class{Mailbox} subclasses, set \var{factory} to \code{None}.
+\end{classdesc}
+
+Maildir is a directory-based mailbox format invented for the qmail mail
+transfer agent and now widely supported by other programs. Messages in a
+Maildir mailbox are stored in separate files within a common directory
+structure. This design allows Maildir mailboxes to be accessed and modified by
+multiple unrelated programs without data corruption, so file locking is
+unnecessary.
+
+Maildir mailboxes contain three subdirectories, namely: \file{tmp}, \file{new},
+and \file{cur}. Messages are created momentarily in the \file{tmp} subdirectory
+and then moved to the \file{new} subdirectory to finalize delivery. A mail user
+agent may subsequently move the message to the \file{cur} subdirectory and
+store information about the state of the message in a special "info" section
+appended to its file name.
+
+Folders of the style introduced by the Courier mail transfer agent are also
+supported. Any subdirectory of the main mailbox is considered a folder if
+\character{.} is the first character in its name. Folder names are represented
+by \class{Maildir} without the leading \character{.}. Each folder is itself a
+Maildir mailbox but should not contain other folders. Instead, a logical
+nesting is indicated using \character{.} to delimit levels, e.g.,
+"Archived.2005.07".
+
+\begin{notice}
+The Maildir specification requires the use of a colon (\character{:}) in
+certain message file names. However, some operating systems do not permit this
+character in file names, If you wish to use a Maildir-like format on such an
+operating system, you should specify another character to use instead. The
+exclamation point (\character{!}) is a popular choice. For example:
+\begin{verbatim}
+import mailbox
+mailbox.Maildir.colon = '!'
+\end{verbatim}
+The \member{colon} attribute may also be set on a per-instance basis.
+\end{notice}
+
+\class{Maildir} instances have all of the methods of \class{Mailbox} in
+addition to the following:
+
+\begin{methoddesc}{list_folders}{}
+Return a list of the names of all folders.
+\end{methoddesc}
+
+\begin{methoddesc}{get_folder}{folder}
+Return a \class{Maildir} instance representing the folder whose name is
+\var{folder}. A \exception{NoSuchMailboxError} exception is raised if the
+folder does not exist.
+\end{methoddesc}
+
+\begin{methoddesc}{add_folder}{folder}
+Create a folder whose name is \var{folder} and return a \class{Maildir}
+instance representing it.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_folder}{folder}
+Delete the folder whose name is \var{folder}. If the folder contains any
+messages, a \exception{NotEmptyError} exception will be raised and the folder
+will not be deleted.
+\end{methoddesc}
+
+\begin{methoddesc}{clean}{}
+Delete temporary files from the mailbox that have not been accessed in the
+last 36 hours. The Maildir specification says that mail-reading programs
+should do this occasionally.
+\end{methoddesc}
+
+Some \class{Mailbox} methods implemented by \class{Maildir} deserve special
+remarks:
+
+\begin{methoddesc}{add}{message}
+\methodline[Maildir]{__setitem__}{key, message}
+\methodline[Maildir]{update}{arg}
+\warning{These methods generate unique file names based upon the current
+process ID. When using multiple threads, undetected name clashes may occur and
+cause corruption of the mailbox unless threads are coordinated to avoid using
+these methods to manipulate the same mailbox simultaneously.}
+\end{methoddesc}
+
+\begin{methoddesc}{flush}{}
+All changes to Maildir mailboxes are immediately applied, so this method does
+nothing.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+\methodline{unlock}{}
+Maildir mailboxes do not support (or require) locking, so these methods do
+nothing. 
+\end{methoddesc}
+
+\begin{methoddesc}{close}{}
+\class{Maildir} instances do not keep any open files and the underlying
+mailboxes do not support locking, so this method does nothing.
+\end{methoddesc}
+
+\begin{methoddesc}{get_file}{key}
+Depending upon the host platform, it may not be possible to modify or remove
+the underlying message while the returned file remains open.
+\end{methoddesc}
+
+\begin{seealso}
+    \seelink{http://www.qmail.org/man/man5/maildir.html}{maildir man page from
+    qmail}{The original specification of the format.}
+    \seelink{http://cr.yp.to/proto/maildir.html}{Using maildir format}{Notes
+    on Maildir by its inventor. Includes an updated name-creation scheme and
+    details on "info" semantics.}
+    \seelink{http://www.courier-mta.org/?maildir.html}{maildir man page from
+    Courier}{Another specification of the format. Describes a common extension
+    for supporting folders.}
+\end{seealso}
+
+\subsubsection{\class{mbox}}
+\label{mailbox-mbox}
+
+\begin{classdesc}{mbox}{path\optional{, factory=None\optional{, create=True}}}
+A subclass of \class{Mailbox} for mailboxes in mbox format. Parameter
+\var{factory} is a callable object that accepts a file-like message
+representation (which behaves as if open in binary mode) and returns a custom
+representation. If \var{factory} is \code{None}, \class{mboxMessage} is used as
+the default message representation. If \var{create} is \code{True}, the mailbox
+is created if it does not exist.
+\end{classdesc}
+
+The mbox format is the classic format for storing mail on \UNIX{} systems. All
+messages in an mbox mailbox are stored in a single file with the beginning of
+each message indicated by a line whose first five characters are "From~".
+
+Several variations of the mbox format exist to address perceived shortcomings
+in the original. In the interest of compatibility, \class{mbox} implements the
+original format, which is sometimes referred to as \dfn{mboxo}. This means that
+the \mailheader{Content-Length} header, if present, is ignored and that any
+occurrences of "From~" at the beginning of a line in a message body are
+transformed to ">From~" when storing the message, although occurences of
+">From~" are not transformed to "From~" when reading the message.
+
+Some \class{Mailbox} methods implemented by \class{mbox} deserve special
+remarks:
+
+\begin{methoddesc}{get_file}{key}
+Using the file after calling \method{flush()} or \method{close()} on the
+\class{mbox} instance may yield unpredictable results or raise an exception.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+\methodline{unlock}{}
+Three locking mechanisms are used---dot locking and, if available, the
+\cfunction{flock()} and \cfunction{lockf()} system calls.
+\end{methoddesc}
+
+\begin{seealso}
+    \seelink{http://www.qmail.org/man/man5/mbox.html}{mbox man page from
+    qmail}{A specification of the format and its variations.}
+    \seelink{http://www.tin.org/bin/man.cgi?section=5\&topic=mbox}{mbox man
+    page from tin}{Another specification of the format, with details on
+    locking.}
+    \seelink{http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html}
+    {Configuring Netscape Mail on \UNIX{}: Why The Content-Length Format is
+    Bad}{An argument for using the original mbox format rather than a
+    variation.}
+    \seelink{http://homepages.tesco.net./\tilde{}J.deBoynePollard/FGA/mail-mbox-formats.html}
+    {"mbox" is a family of several mutually incompatible mailbox formats}{A
+    history of mbox variations.}
+\end{seealso}
+
+\subsubsection{\class{MH}}
+\label{mailbox-mh}
+
+\begin{classdesc}{MH}{path\optional{, factory=None\optional{, create=True}}}
+A subclass of \class{Mailbox} for mailboxes in MH format. Parameter
+\var{factory} is a callable object that accepts a file-like message
+representation (which behaves as if open in binary mode) and returns a custom
+representation. If \var{factory} is \code{None}, \class{MHMessage} is used as
+the default message representation. If \var{create} is \code{True}, the mailbox
+is created if it does not exist.
+\end{classdesc}
+
+MH is a directory-based mailbox format invented for the MH Message Handling
+System, a mail user agent. Each message in an MH mailbox resides in its own
+file. An MH mailbox may contain other MH mailboxes (called \dfn{folders}) in
+addition to messages. Folders may be nested indefinitely. MH mailboxes also
+support \dfn{sequences}, which are named lists used to logically group messages
+without moving them to sub-folders. Sequences are defined in a file called
+\file{.mh_sequences} in each folder.
+
+The \class{MH} class manipulates MH mailboxes, but it does not attempt to
+emulate all of \program{mh}'s behaviors. In particular, it does not modify and
+is not affected by the \file{context} or \file{.mh_profile} files that are used
+by \program{mh} to store its state and configuration.
+
+\class{MH} instances have all of the methods of \class{Mailbox} in addition to
+the following:
+
+\begin{methoddesc}{list_folders}{}
+Return a list of the names of all folders.
+\end{methoddesc}
+
+\begin{methoddesc}{get_folder}{folder}
+Return an \class{MH} instance representing the folder whose name is
+\var{folder}. A \exception{NoSuchMailboxError} exception is raised if the
+folder does not exist.
+\end{methoddesc}
+
+\begin{methoddesc}{add_folder}{folder}
+Create a folder whose name is \var{folder} and return an \class{MH} instance
+representing it.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_folder}{folder}
+Delete the folder whose name is \var{folder}. If the folder contains any
+messages, a \exception{NotEmptyError} exception will be raised and the folder
+will not be deleted.
+\end{methoddesc}
+
+\begin{methoddesc}{get_sequences}{}
+Return a dictionary of sequence names mapped to key lists. If there are no
+sequences, the empty dictionary is returned.
+\end{methoddesc}
+
+\begin{methoddesc}{set_sequences}{sequences}
+Re-define the sequences that exist in the mailbox based upon \var{sequences}, a
+dictionary of names mapped to key lists, like returned by
+\method{get_sequences()}.
+\end{methoddesc}
+
+\begin{methoddesc}{pack}{}
+Rename messages in the mailbox as necessary to eliminate gaps in numbering.
+Entries in the sequences list are updated correspondingly. \note{Already-issued
+keys are invalidated by this operation and should not be subsequently used.}
+\end{methoddesc}
+
+Some \class{Mailbox} methods implemented by \class{MH} deserve special remarks:
+
+\begin{methoddesc}{remove}{key}
+\methodline{__delitem__}{key}
+\methodline{discard}{key}
+These methods immediately delete the message. The MH convention of marking a
+message for deletion by prepending a comma to its name is not used.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+\methodline{unlock}{}
+Three locking mechanisms are used---dot locking and, if available, the
+\cfunction{flock()} and \cfunction{lockf()} system calls. For MH mailboxes,
+locking the mailbox means locking the \file{.mh_sequences} file and, only for
+the duration of any operations that affect them, locking individual message
+files.
+\end{methoddesc}
+
+\begin{methoddesc}{get_file}{key}
+Depending upon the host platform, it may not be possible to remove the
+underlying message while the returned file remains open.
+\end{methoddesc}
+
+\begin{methoddesc}{flush}{}
+All changes to MH mailboxes are immediately applied, so this method does
+nothing.
+\end{methoddesc}
+
+\begin{methoddesc}{close}{}
+\class{MH} instances do not keep any open files, so this method is equivelant
+to \method{unlock()}.
+\end{methoddesc}
+
+\begin{seealso}
+\seelink{http://www.nongnu.org/nmh/}{nmh - Message Handling System}{Home page
+of \program{nmh}, an updated version of the original \program{mh}.}
+\seelink{http://www.ics.uci.edu/\tilde{}mh/book/}{MH \& nmh: Email for Users \&
+Programmers}{A GPL-licensed book on \program{mh} and \program{nmh}, with some
+information on the mailbox format.}
+\end{seealso}
+
+\subsubsection{\class{Babyl}}
+\label{mailbox-babyl}
+
+\begin{classdesc}{Babyl}{path\optional{, factory=None\optional{, create=True}}}
+A subclass of \class{Mailbox} for mailboxes in Babyl format. Parameter
+\var{factory} is a callable object that accepts a file-like message
+representation (which behaves as if open in binary mode) and returns a custom
+representation. If \var{factory} is \code{None}, \class{BabylMessage} is used
+as the default message representation. If \var{create} is \code{True}, the
+mailbox is created if it does not exist.
+\end{classdesc}
+
+Babyl is a single-file mailbox format used by the Rmail mail user agent
+included with Emacs. The beginning of a message is indicated by a line
+containing the two characters Control-Underscore
+(\character{\textbackslash037}) and Control-L (\character{\textbackslash014}).
+The end of a message is indicated by the start of the next message or, in the
+case of the last message, a line containing a Control-Underscore
+(\character{\textbackslash037}) character.
+
+Messages in a Babyl mailbox have two sets of headers, original headers and
+so-called visible headers. Visible headers are typically a subset of the
+original headers that have been reformatted or abridged to be more attractive.
+Each message in a Babyl mailbox also has an accompanying list of \dfn{labels},
+or short strings that record extra information about the message, and a list of
+all user-defined labels found in the mailbox is kept in the Babyl options
+section.
+
+\class{Babyl} instances have all of the methods of \class{Mailbox} in addition
+to the following:
+
+\begin{methoddesc}{get_labels}{}
+Return a list of the names of all user-defined labels used in the mailbox.
+\note{The actual messages are inspected to determine which labels exist in the
+mailbox rather than consulting the list of labels in the Babyl options section,
+but the Babyl section is updated whenever the mailbox is modified.}
+\end{methoddesc}
+
+Some \class{Mailbox} methods implemented by \class{Babyl} deserve special
+remarks:
+
+\begin{methoddesc}{get_file}{key}
+In Babyl mailboxes, the headers of a message are not stored contiguously with
+the body of the message. To generate a file-like representation, the headers
+and body are copied together into a \class{StringIO} instance (from the
+\module{StringIO} module), which has an API identical to that of a file. As a
+result, the file-like object is truly independent of the underlying mailbox but
+does not save memory compared to a string representation.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+\methodline{unlock}{}
+Three locking mechanisms are used---dot locking and, if available, the
+\cfunction{flock()} and \cfunction{lockf()} system calls.
+\end{methoddesc}
+
+\begin{seealso}
+\seelink{http://quimby.gnus.org/notes/BABYL}{Format of Version 5 Babyl Files}{A
+specification of the Babyl format.}
+\seelink{http://www.gnu.org/software/emacs/manual/html_node/Rmail.html}{Reading
+Mail with Rmail}{The Rmail manual, with some information on Babyl semantics.}
+\end{seealso}
+
+\subsubsection{\class{MMDF}}
+\label{mailbox-mmdf}
+
+\begin{classdesc}{MMDF}{path\optional{, factory=None\optional{, create=True}}}
+A subclass of \class{Mailbox} for mailboxes in MMDF format. Parameter
+\var{factory} is a callable object that accepts a file-like message
+representation (which behaves as if open in binary mode) and returns a custom
+representation. If \var{factory} is \code{None}, \class{MMDFMessage} is used as
+the default message representation. If \var{create} is \code{True}, the mailbox
+is created if it does not exist.
+\end{classdesc}
+
+MMDF is a single-file mailbox format invented for the Multichannel Memorandum
+Distribution Facility, a mail transfer agent. Each message is in the same form
+as an mbox message but is bracketed before and after by lines containing four
+Control-A (\character{\textbackslash001}) characters. As with the mbox format,
+the beginning of each message is indicated by a line whose first five
+characters are "From~", but additional occurrences of "From~" are not
+transformed to ">From~" when storing messages because the extra message
+separator lines prevent mistaking such occurrences for the starts of subsequent
+messages.
+
+Some \class{Mailbox} methods implemented by \class{MMDF} deserve special
+remarks:
+
+\begin{methoddesc}{get_file}{key}
+Using the file after calling \method{flush()} or \method{close()} on the
+\class{MMDF} instance may yield unpredictable results or raise an exception.
+\end{methoddesc}
+
+\begin{methoddesc}{lock}{}
+\methodline{unlock}{}
+Three locking mechanisms are used---dot locking and, if available, the
+\cfunction{flock()} and \cfunction{lockf()} system calls.
+\end{methoddesc}
+
+\begin{seealso}
+\seelink{http://www.tin.org/bin/man.cgi?section=5\&topic=mmdf}{mmdf man page
+from tin}{A specification of MMDF format from the documentation of tin, a
+newsreader.}
+\seelink{http://en.wikipedia.org/wiki/MMDF}{MMDF}{A Wikipedia article
+describing the Multichannel Memorandum Distribution Facility.}
+\end{seealso}
+
+\subsection{\class{Message} objects}
+\label{mailbox-message-objects}
+
+\begin{classdesc}{Message}{\optional{message}}
+A subclass of the \module{email.Message} module's \class{Message}. Subclasses
+of \class{mailbox.Message} add mailbox-format-specific state and behavior.
+
+If \var{message} is omitted, the new instance is created in a default, empty
+state. If \var{message} is an \class{email.Message.Message} instance, its
+contents are copied; furthermore, any format-specific information is converted
+insofar as possible if \var{message} is a \class{Message} instance. If
+\var{message} is a string or a file, it should contain an \rfc{2822}-compliant
+message, which is read and parsed.
+\end{classdesc}
+
+The format-specific state and behaviors offered by subclasses vary, but in
+general it is only the properties that are not specific to a particular mailbox
+that are supported (although presumably the properties are specific to a
+particular mailbox format). For example, file offsets for single-file mailbox
+formats and file names for directory-based mailbox formats are not retained,
+because they are only applicable to the original mailbox. But state such as
+whether a message has been read by the user or marked as important is retained,
+because it applies to the message itself.
+
+There is no requirement that \class{Message} instances be used to represent
+messages retrieved using \class{Mailbox} instances. In some situations, the
+time and memory required to generate \class{Message} representations might not
+not acceptable. For such situations, \class{Mailbox} instances also offer
+string and file-like representations, and a custom message factory may be
+specified when a \class{Mailbox} instance is initialized. 
+
+\subsubsection{\class{MaildirMessage}}
+\label{mailbox-maildirmessage}
+
+\begin{classdesc}{MaildirMessage}{\optional{message}}
+A message with Maildir-specific behaviors. Parameter \var{message}
+has the same meaning as with the \class{Message} constructor.
+\end{classdesc}
+
+Typically, a mail user agent application moves all of the messages in the
+\file{new} subdirectory to the \file{cur} subdirectory after the first time the
+user opens and closes the mailbox, recording that the messages are old whether
+or not they've actually been read. Each message in \file{cur} has an "info"
+section added to its file name to store information about its state. (Some mail
+readers may also add an "info" section to messages in \file{new}.) The "info"
+section may take one of two forms: it may contain "2," followed by a list of
+standardized flags (e.g., "2,FR") or it may contain "1," followed by so-called
+experimental information. Standard flags for Maildir messages are as follows:
+
+\begin{tableiii}{l|l|l}{textrm}{Flag}{Meaning}{Explanation}
+\lineiii{D}{Draft}{Under composition}
+\lineiii{F}{Flagged}{Marked as important}
+\lineiii{P}{Passed}{Forwarded, resent, or bounced}
+\lineiii{R}{Replied}{Replied to}
+\lineiii{S}{Seen}{Read}
+\lineiii{T}{Trashed}{Marked for subsequent deletion}
+\end{tableiii}
+
+\class{MaildirMessage} instances offer the following methods:
+
+\begin{methoddesc}{get_subdir}{}
+Return either "new" (if the message should be stored in the \file{new}
+subdirectory) or "cur" (if the message should be stored in the \file{cur}
+subdirectory). \note{A message is typically moved from \file{new} to \file{cur}
+after its mailbox has been accessed, whether or not the message is has been
+read. A message \code{msg} has been read if \code{"S" not in msg.get_flags()}
+is \code{True}.}
+\end{methoddesc}
+
+\begin{methoddesc}{set_subdir}{subdir}
+Set the subdirectory the message should be stored in. Parameter \var{subdir}
+must be either "new" or "cur".
+\end{methoddesc}
+
+\begin{methoddesc}{get_flags}{}
+Return a string specifying the flags that are currently set. If the message
+complies with the standard Maildir format, the result is the concatenation in
+alphabetical order of zero or one occurrence of each of \character{D},
+\character{F}, \character{P}, \character{R}, \character{S}, and \character{T}.
+The empty string is returned if no flags are set or if "info" contains
+experimental semantics.
+\end{methoddesc}
+
+\begin{methoddesc}{set_flags}{flags}
+Set the flags specified by \var{flags} and unset all others.
+\end{methoddesc}
+
+\begin{methoddesc}{add_flag}{flag}
+Set the flag(s) specified by \var{flag} without changing other flags. To add
+more than one flag at a time, \var{flag} may be a string of more than one
+character. The current "info" is overwritten whether or not it contains
+experimental information rather than
+flags.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_flag}{flag}
+Unset the flag(s) specified by \var{flag} without changing other flags. To
+remove more than one flag at a time, \var{flag} maybe a string of more than one
+character. If "info" contains experimental information rather than flags, the
+current "info" is not modified.
+\end{methoddesc}
+
+\begin{methoddesc}{get_date}{}
+Return the delivery date of the message as a floating-point number representing
+seconds since the epoch.
+\end{methoddesc}
+
+\begin{methoddesc}{set_date}{date}
+Set the delivery date of the message to \var{date}, a floating-point number
+representing seconds since the epoch.
+\end{methoddesc}
+
+\begin{methoddesc}{get_info}{}
+Return a string containing the "info" for a message. This is useful for
+accessing and modifying "info" that is experimental (i.e., not a list of
+flags).
+\end{methoddesc}
+
+\begin{methoddesc}{set_info}{info}
+Set "info" to \var{info}, which should be a string.
+\end{methoddesc}
+
+When a \class{MaildirMessage} instance is created based upon an
+\class{mboxMessage} or \class{MMDFMessage} instance, the \mailheader{Status}
+and \mailheader{X-Status} headers are omitted and the following conversions
+take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{mboxMessage} or \class{MMDFMessage} state}
+\lineii{"cur" subdirectory}{O flag}
+\lineii{F flag}{F flag}
+\lineii{R flag}{A flag}
+\lineii{S flag}{R flag}
+\lineii{T flag}{D flag}
+\end{tableii}
+
+When a \class{MaildirMessage} instance is created based upon an
+\class{MHMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MHMessage} state}
+\lineii{"cur" subdirectory}{"unseen" sequence}
+\lineii{"cur" subdirectory and S flag}{no "unseen" sequence}
+\lineii{F flag}{"flagged" sequence}
+\lineii{R flag}{"replied" sequence}
+\end{tableii}
+
+When a \class{MaildirMessage} instance is created based upon a
+\class{BabylMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{BabylMessage} state}
+\lineii{"cur" subdirectory}{"unseen" label}
+\lineii{"cur" subdirectory and S flag}{no "unseen" label}
+\lineii{P flag}{"forwarded" or "resent" label}
+\lineii{R flag}{"answered" label}
+\lineii{T flag}{"deleted" label}
+\end{tableii}
+
+\subsubsection{\class{mboxMessage}}
+\label{mailbox-mboxmessage}
+
+\begin{classdesc}{mboxMessage}{\optional{message}}
+A message with mbox-specific behaviors. Parameter \var{message} has the same
+meaning as with the \class{Message} constructor.
+\end{classdesc}
+
+Messages in an mbox mailbox are stored together in a single file. The sender's
+envelope address and the time of delivery are typically stored in a line
+beginning with "From~" that is used to indicate the start of a message, though
+there is considerable variation in the exact format of this data among mbox
+implementations. Flags that indicate the state of the message, such as whether
+it has been read or marked as important, are typically stored in
+\mailheader{Status} and \mailheader{X-Status} headers.
+
+Conventional flags for mbox messages are as follows:
+
+\begin{tableiii}{l|l|l}{textrm}{Flag}{Meaning}{Explanation}
+\lineiii{R}{Read}{Read}
+\lineiii{O}{Old}{Previously detected by MUA}
+\lineiii{D}{Deleted}{Marked for subsequent deletion}
+\lineiii{F}{Flagged}{Marked as important}
+\lineiii{A}{Answered}{Replied to}
+\end{tableiii}
+
+The "R" and "O" flags are stored in the \mailheader{Status} header, and the
+"D", "F", and "A" flags are stored in the \mailheader{X-Status} header. The
+flags and headers typically appear in the order mentioned.
+
+\class{mboxMessage} instances offer the following methods:
+
+\begin{methoddesc}{get_from}{}
+Return a string representing the "From~" line that marks the start of the
+message in an mbox mailbox. The leading "From~" and the trailing newline are
+excluded.
+\end{methoddesc}
+
+\begin{methoddesc}{set_from}{from_\optional{, time_=None}}
+Set the "From~" line to \var{from_}, which should be specified without a
+leading "From~" or trailing newline. For convenience, \var{time_} may be
+specified and will be formatted appropriately and appended to \var{from_}. If
+\var{time_} is specified, it should be a \class{struct_time} instance, a tuple
+suitable for passing to \method{time.strftime()}, or \code{True} (to use
+\method{time.gmtime()}).
+\end{methoddesc}
+
+\begin{methoddesc}{get_flags}{}
+Return a string specifying the flags that are currently set. If the message
+complies with the conventional format, the result is the concatenation in the
+following order of zero or one occurrence of each of \character{R},
+\character{O}, \character{D}, \character{F}, and \character{A}.
+\end{methoddesc}
+
+\begin{methoddesc}{set_flags}{flags}
+Set the flags specified by \var{flags} and unset all others. Parameter
+\var{flags} should be the concatenation in any order of zero or more
+occurrences of each of \character{R}, \character{O}, \character{D},
+\character{F}, and \character{A}.
+\end{methoddesc}
+
+\begin{methoddesc}{add_flag}{flag}
+Set the flag(s) specified by \var{flag} without changing other flags. To add
+more than one flag at a time, \var{flag} may be a string of more than one
+character.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_flag}{flag}
+Unset the flag(s) specified by \var{flag} without changing other flags. To
+remove more than one flag at a time, \var{flag} maybe a string of more than one
+character.
+\end{methoddesc}
+
+When an \class{mboxMessage} instance is created based upon a
+\class{MaildirMessage} instance, a "From~" line is generated based upon the
+\class{MaildirMessage} instance's delivery date, and the following conversions
+take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MaildirMessage} state}
+\lineii{R flag}{S flag}
+\lineii{O flag}{"cur" subdirectory}
+\lineii{D flag}{T flag}
+\lineii{F flag}{F flag}
+\lineii{A flag}{R flag}
+\end{tableii}
+
+When an \class{mboxMessage} instance is created based upon an \class{MHMessage}
+instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MHMessage} state}
+\lineii{R flag and O flag}{no "unseen" sequence}
+\lineii{O flag}{"unseen" sequence}
+\lineii{F flag}{"flagged" sequence}
+\lineii{A flag}{"replied" sequence}
+\end{tableii}
+
+When an \class{mboxMessage} instance is created based upon a
+\class{BabylMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{BabylMessage} state}
+\lineii{R flag and O flag}{no "unseen" label}
+\lineii{O flag}{"unseen" label}
+\lineii{D flag}{"deleted" label}
+\lineii{A flag}{"answered" label}
+\end{tableii}
+
+When a \class{Message} instance is created based upon an \class{MMDFMessage}
+instance, the "From~" line is copied and all flags directly correspond:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MMDFMessage} state}
+\lineii{R flag}{R flag}
+\lineii{O flag}{O flag}
+\lineii{D flag}{D flag}
+\lineii{F flag}{F flag}
+\lineii{A flag}{A flag}
+\end{tableii}
+
+\subsubsection{\class{MHMessage}}
+\label{mailbox-mhmessage}
+
+\begin{classdesc}{MHMessage}{\optional{message}}
+A message with MH-specific behaviors. Parameter \var{message} has the same
+meaning as with the \class{Message} constructor.
+\end{classdesc}
+
+MH messages do not support marks or flags in the traditional sense, but they do
+support sequences, which are logical groupings of arbitrary messages. Some mail
+reading programs (although not the standard \program{mh} and \program{nmh}) use
+sequences in much the same way flags are used with other formats, as follows:
+
+\begin{tableii}{l|l}{textrm}{Sequence}{Explanation}
+\lineii{unseen}{Not read, but previously detected by MUA}
+\lineii{replied}{Replied to}
+\lineii{flagged}{Marked as important}
+\end{tableii}
+
+\class{MHMessage} instances offer the following methods:
+
+\begin{methoddesc}{get_sequences}{}
+Return a list of the names of sequences that include this message.
+\end{methoddesc}
+
+\begin{methoddesc}{set_sequences}{sequences}
+Set the list of sequences that include this message.
+\end{methoddesc}
+
+\begin{methoddesc}{add_sequence}{sequence}
+Add \var{sequence} to the list of sequences that include this message.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_sequence}{sequence}
+Remove \var{sequence} from the list of sequences that include this message.
+\end{methoddesc}
+
+When an \class{MHMessage} instance is created based upon a
+\class{MaildirMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MaildirMessage} state}
+\lineii{"unseen" sequence}{no S flag}
+\lineii{"replied" sequence}{R flag}
+\lineii{"flagged" sequence}{F flag}
+\end{tableii}
+
+When an \class{MHMessage} instance is created based upon an \class{mboxMessage}
+or \class{MMDFMessage} instance, the \mailheader{Status} and
+\mailheader{X-Status} headers are omitted and the following conversions take
+place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{mboxMessage} or \class{MMDFMessage} state}
+\lineii{"unseen" sequence}{no R flag}
+\lineii{"replied" sequence}{A flag}
+\lineii{"flagged" sequence}{F flag}
+\end{tableii}
+
+When an \class{MHMessage} instance is created based upon a \class{BabylMessage}
+instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{BabylMessage} state}
+\lineii{"unseen" sequence}{"unseen" label}
+\lineii{"replied" sequence}{"answered" label}
+\end{tableii}
+
+\subsubsection{\class{BabylMessage}}
+\label{mailbox-babylmessage}
+
+\begin{classdesc}{BabylMessage}{\optional{message}}
+A message with Babyl-specific behaviors. Parameter \var{message} has the same
+meaning as with the \class{Message} constructor.
+\end{classdesc}
+
+Certain message labels, called \dfn{attributes}, are defined by convention to
+have special meanings. The attributes are as follows:
+
+\begin{tableii}{l|l}{textrm}{Label}{Explanation}
+\lineii{unseen}{Not read, but previously detected by MUA}
+\lineii{deleted}{Marked for subsequent deletion}
+\lineii{filed}{Copied to another file or mailbox}
+\lineii{answered}{Replied to}
+\lineii{forwarded}{Forwarded}
+\lineii{edited}{Modified by the user}
+\lineii{resent}{Resent}
+\end{tableii}
+
+By default, Rmail displays only
+visible headers. The \class{BabylMessage} class, though, uses the original
+headers because they are more complete. Visible headers may be accessed
+explicitly if desired.
+
+\class{BabylMessage} instances offer the following methods:
+
+\begin{methoddesc}{get_labels}{}
+Return a list of labels on the message.
+\end{methoddesc}
+
+\begin{methoddesc}{set_labels}{labels}
+Set the list of labels on the message to \var{labels}.
+\end{methoddesc}
+
+\begin{methoddesc}{add_label}{label}
+Add \var{label} to the list of labels on the message.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_label}{label}
+Remove \var{label} from the list of labels on the message.
+\end{methoddesc}
+
+\begin{methoddesc}{get_visible}{}
+Return an \class{Message} instance whose headers are the message's visible
+headers and whose body is empty.
+\end{methoddesc}
+
+\begin{methoddesc}{set_visible}{visible}
+Set the message's visible headers to be the same as the headers in
+\var{message}. Parameter \var{visible} should be a \class{Message} instance, an
+\class{email.Message.Message} instance, a string, or a file-like object (which
+should be open in text mode).
+\end{methoddesc}
+
+\begin{methoddesc}{update_visible}{}
+When a \class{BabylMessage} instance's original headers are modified, the
+visible headers are not automatically modified to correspond. This method
+updates the visible headers as follows: each visible header with a
+corresponding original header is set to the value of the original header, each
+visible header without a corresponding original header is removed, and any of
+\mailheader{Date}, \mailheader{From}, \mailheader{Reply-To}, \mailheader{To},
+\mailheader{CC}, and \mailheader{Subject} that are present in the original
+headers but not the visible headers are added to the visible headers.
+\end{methoddesc}
+
+When a \class{BabylMessage} instance is created based upon a
+\class{MaildirMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MaildirMessage} state}
+\lineii{"unseen" label}{no S flag}
+\lineii{"deleted" label}{T flag}
+\lineii{"answered" label}{R flag}
+\lineii{"forwarded" label}{P flag}
+\end{tableii}
+
+When a \class{BabylMessage} instance is created based upon an
+\class{mboxMessage} or \class{MMDFMessage} instance, the \mailheader{Status}
+and \mailheader{X-Status} headers are omitted and the following conversions
+take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{mboxMessage} or \class{MMDFMessage} state}
+\lineii{"unseen" label}{no R flag}
+\lineii{"deleted" label}{D flag}
+\lineii{"answered" label}{A flag}
+\end{tableii}
+
+When a \class{BabylMessage} instance is created based upon an \class{MHMessage}
+instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MHMessage} state}
+\lineii{"unseen" label}{"unseen" sequence}
+\lineii{"answered" label}{"replied" sequence}
+\end{tableii}
+
+\subsubsection{\class{MMDFMessage}}
+\label{mailbox-mmdfmessage}
+
+\begin{classdesc}{MMDFMessage}{\optional{message}}
+A message with MMDF-specific behaviors. Parameter \var{message} has the same
+meaning as with the \class{Message} constructor.
+\end{classdesc}
+
+As with message in an mbox mailbox, MMDF messages are stored with the sender's
+address and the delivery date in an initial line beginning with "From ".
+Likewise, flags that indicate the state of the message are typically stored in
+\mailheader{Status} and \mailheader{X-Status} headers.
+
+Conventional flags for MMDF messages are identical to those of mbox message and
+are as follows:
+
+\begin{tableiii}{l|l|l}{textrm}{Flag}{Meaning}{Explanation}
+\lineiii{R}{Read}{Read}
+\lineiii{O}{Old}{Previously detected by MUA}
+\lineiii{D}{Deleted}{Marked for subsequent deletion}
+\lineiii{F}{Flagged}{Marked as important}
+\lineiii{A}{Answered}{Replied to}
+\end{tableiii}
+
+The "R" and "O" flags are stored in the \mailheader{Status} header, and the
+"D", "F", and "A" flags are stored in the \mailheader{X-Status} header. The
+flags and headers typically appear in the order mentioned.
+
+\class{MMDFMessage} instances offer the following methods, which are identical
+to those offered by \class{mboxMessage}:
+
+\begin{methoddesc}{get_from}{}
+Return a string representing the "From~" line that marks the start of the
+message in an mbox mailbox. The leading "From~" and the trailing newline are
+excluded.
+\end{methoddesc}
+
+\begin{methoddesc}{set_from}{from_\optional{, time_=None}}
+Set the "From~" line to \var{from_}, which should be specified without a
+leading "From~" or trailing newline. For convenience, \var{time_} may be
+specified and will be formatted appropriately and appended to \var{from_}. If
+\var{time_} is specified, it should be a \class{struct_time} instance, a tuple
+suitable for passing to \method{time.strftime()}, or \code{True} (to use
+\method{time.gmtime()}).
+\end{methoddesc}
+
+\begin{methoddesc}{get_flags}{}
+Return a string specifying the flags that are currently set. If the message
+complies with the conventional format, the result is the concatenation in the
+following order of zero or one occurrence of each of \character{R},
+\character{O}, \character{D}, \character{F}, and \character{A}.
+\end{methoddesc}
+
+\begin{methoddesc}{set_flags}{flags}
+Set the flags specified by \var{flags} and unset all others. Parameter
+\var{flags} should be the concatenation in any order of zero or more
+occurrences of each of \character{R}, \character{O}, \character{D},
+\character{F}, and \character{A}.
+\end{methoddesc}
+
+\begin{methoddesc}{add_flag}{flag}
+Set the flag(s) specified by \var{flag} without changing other flags. To add
+more than one flag at a time, \var{flag} may be a string of more than one
+character.
+\end{methoddesc}
+
+\begin{methoddesc}{remove_flag}{flag}
+Unset the flag(s) specified by \var{flag} without changing other flags. To
+remove more than one flag at a time, \var{flag} maybe a string of more than one
+character.
+\end{methoddesc}
+
+When an \class{MMDFMessage} instance is created based upon a
+\class{MaildirMessage} instance, a "From~" line is generated based upon the
+\class{MaildirMessage} instance's delivery date, and the following conversions
+take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MaildirMessage} state}
+\lineii{R flag}{S flag}
+\lineii{O flag}{"cur" subdirectory}
+\lineii{D flag}{T flag}
+\lineii{F flag}{F flag}
+\lineii{A flag}{R flag}
+\end{tableii}
+
+When an \class{MMDFMessage} instance is created based upon an \class{MHMessage}
+instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{MHMessage} state}
+\lineii{R flag and O flag}{no "unseen" sequence}
+\lineii{O flag}{"unseen" sequence}
+\lineii{F flag}{"flagged" sequence}
+\lineii{A flag}{"replied" sequence}
+\end{tableii}
+
+When an \class{MMDFMessage} instance is created based upon a
+\class{BabylMessage} instance, the following conversions take place:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{BabylMessage} state}
+\lineii{R flag and O flag}{no "unseen" label}
+\lineii{O flag}{"unseen" label}
+\lineii{D flag}{"deleted" label}
+\lineii{A flag}{"answered" label}
+\end{tableii}
+
+When an \class{MMDFMessage} instance is created based upon an
+\class{mboxMessage} instance, the "From~" line is copied and all flags directly
+correspond:
+
+\begin{tableii}{l|l}{textrm}
+    {Resulting state}{\class{mboxMessage} state}
+\lineii{R flag}{R flag}
+\lineii{O flag}{O flag}
+\lineii{D flag}{D flag}
+\lineii{F flag}{F flag}
+\lineii{A flag}{A flag}
+\end{tableii}
+
+\subsection{Exceptions}
+\label{mailbox-deprecated}
+
+The following exception classes are defined in the \module{mailbox} module:
+
+\begin{classdesc}{Error}{}
+The based class for all other module-specific exceptions.
+\end{classdesc}
+
+\begin{classdesc}{NoSuchMailboxError}{}
+Raised when a mailbox is expected but is not found, such as when instantiating
+a \class{Mailbox} subclass with a path that does not exist (and with the
+\var{create} parameter set to \code{False}), or when opening a folder that does
+not exist.
+\end{classdesc}
+
+\begin{classdesc}{NotEmptyErrorError}{}
+Raised when a mailbox is not empty but is expected to be, such as when deleting
+a folder that contains messages.
+\end{classdesc}
+
+\begin{classdesc}{ExternalClashError}{}
+Raised when some mailbox-related condition beyond the control of the program
+causes it to be unable to proceed, such as when failing to acquire a lock that
+another program already holds a lock, or when a uniquely-generated file name
+already exists.
+\end{classdesc}
+
+\begin{classdesc}{FormatError}{}
+Raised when the data in a file cannot be parsed, such as when an \class{MH}
+instance attempts to read a corrupted \file{.mh_sequences} file.
+\end{classdesc}
+
+\subsection{Deprecated classes and methods}
+\label{mailbox-deprecated}
+
+Older versions of the \module{mailbox} module do not support modification of
+mailboxes, such as adding or removing message, and do not provide classes to
+represent format-specific message properties. For backward compatibility, the
+older mailbox classes are still available, but the newer classes should be used
+in preference to them.
+
+Older mailbox objects support only iteration and provide a single public
+method:
+
+\begin{methoddesc}{next}{}
+Return the next message in the mailbox, created with the optional \var{factory}
+argument passed into the mailbox object's constructor. By default this is an
+\class{rfc822.Message} object (see the \refmodule{rfc822} module).  Depending
+on the mailbox implementation the \var{fp} attribute of this object may be a
+true file object or a class instance simulating a file object, taking care of
+things like message boundaries if multiple mail messages are contained in a
+single file, etc.  If no more messages are available, this method returns
+\code{None}.
+\end{methoddesc}
+
+Most of the older mailbox classes have names that differ from the current
+mailbox class names, except for \class{Maildir}. For this reason, the new
+\class{Maildir} class defines a \method{next()} method and its constructor
+differs slightly from those of the other new mailbox classes.
+
+The older mailbox classes whose names are not the same as their newer
+counterparts are as follows:
 
 \begin{classdesc}{UnixMailbox}{fp\optional{, factory}}
 Access to a classic \UNIX-style mailbox, where all messages are
@@ -68,12 +1309,6 @@ The name of the mailbox directory is passed in \var{dirname}.
 \var{factory} is as with the \class{UnixMailbox} class.
 \end{classdesc}
 
-\begin{classdesc}{Maildir}{dirname\optional{, factory}}
-Access a Qmail mail directory.  All new and current mail for the
-mailbox specified by \var{dirname} is made available.
-\var{factory} is as with the \class{UnixMailbox} class.
-\end{classdesc}
-
 \begin{classdesc}{BabylMailbox}{fp\optional{, factory}}
 Access a Babyl mailbox, which is similar to an MMDF mailbox.  In
 Babyl format, each message has two sets of headers, the
@@ -89,11 +1324,8 @@ messages start with the EOOH line and end with a line containing only
 \class{UnixMailbox} class.
 \end{classdesc}
 
-Note that because the \refmodule{rfc822} module is deprecated, it is
-recommended that you use the \refmodule{email} package to create
-message objects from a mailbox.  (The default can't be changed for
-backwards compatibility reasons.)  The safest way to do this is with
-bit of code:
+If you wish to use the older mailbox classes with the \module{email} module
+rather than the deprecated \module{rfc822} module, you can do so as follows:
 
 \begin{verbatim}
 import email
@@ -111,11 +1343,8 @@ def msgfactory(fp):
 mbox = mailbox.UnixMailbox(fp, msgfactory)
 \end{verbatim}
 
-The above wrapper is defensive against ill-formed MIME messages in the
-mailbox, but you have to be prepared to receive the empty string from
-the mailbox's \function{next()} method.  On the other hand, if you
-know your mailbox contains only well-formed MIME messages, you can
-simplify this to:
+Alternatively, if you know your mailbox contains only well-formed MIME
+messages, you can simplify this to:
 
 \begin{verbatim}
 import email
@@ -124,35 +1353,57 @@ import mailbox
 mbox = mailbox.UnixMailbox(fp, email.message_from_file)
 \end{verbatim}
 
-\begin{seealso}
-  \seetitle[http://www.qmail.org/man/man5/mbox.html]{mbox -
-            file containing mail messages}{Description of the
-            traditional ``mbox'' mailbox format.}
-  \seetitle[http://www.qmail.org/man/man5/maildir.html]{maildir -
-            directory for incoming mail messages}{Description of the
-            ``maildir'' mailbox format.}
-  \seetitle[http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html]{Configuring
-            Netscape Mail on \UNIX: Why the Content-Length Format is
-            Bad}{A description of problems with relying on the
-            \mailheader{Content-Length} header for messages stored in
-            mailbox files.}
-\end{seealso}
+\subsection{Examples}
+\label{mailbox-examples}
 
+A simple example of printing the subjects of all messages in a mailbox that
+seem interesting:
 
-\subsection{Mailbox Objects \label{mailbox-objects}}
+\begin{verbatim}
+import mailbox
+for message in mailbox.mbox('~/mbox'):
+    subject = message['subject']       # Could possibly be None.
+    if subject and 'python' in subject.lower():
+        print subject
+\end{verbatim}
 
-All implementations of mailbox objects are iterable objects, and
-have one externally visible method.  This method is used by iterators
-created from mailbox objects and may also be used directly.
+A (surprisingly) simple example of copying all mail from a Babyl mailbox to an
+MH mailbox, converting all of the format-specific information that can be
+converted:
 
-\begin{methoddesc}[mailbox]{next}{}
-Return the next message in the mailbox, created with the optional
-\var{factory} argument passed into the mailbox object's constructor.
-By default this is an \class{rfc822.Message}
-object (see the \refmodule{rfc822} module).  Depending on the mailbox
-implementation the \var{fp} attribute of this object may be a true
-file object or a class instance simulating a file object, taking care
-of things like message boundaries if multiple mail messages are
-contained in a single file, etc.  If no more messages are available,
-this method returns \code{None}.
-\end{methoddesc}
+\begin{verbatim}
+import mailbox
+destination = mailbox.MH('~/Mail')
+for message in mailbox.Babyl('~/RMAIL'):
+    destination.add(MHMessage(message))
+\end{verbatim}
+
+An example of sorting mail from numerous mailing lists, being careful to avoid
+mail corruption due to concurrent modification by other programs, mail loss due
+to interruption of the program, or premature termination due to malformed
+messages in the mailbox:
+
+\begin{verbatim}
+import mailbox
+import email.Errors
+list_names = ('python-list', 'python-dev', 'python-bugs')
+boxes = dict((name, mailbox.mbox('~/email/%s' % name)) for name in list_names)
+inbox = mailbox.Maildir('~/Maildir', None)
+for key in inbox.iterkeys():
+    try:
+        message = inbox[key]
+    except email.Errors.MessageParseError:
+        continue                # The message is malformed. Just leave it.
+    for name in list_names:
+        list_id = message['list-id']
+        if list_id and name in list_id:
+            box = boxes[name]
+            box.lock()
+            box.add(message)
+            box.flush()         # Write copy to disk before removing original.
+            box.unlock()
+            inbox.discard(key)
+            break               # Found destination, so stop looking.
+for box in boxes.itervalues():
+    box.close()
+\end{verbatim}

Lib/mailbox.py

 #! /usr/bin/env python
 
-"""Classes to handle Unix style, MMDF style, and MH style mailboxes."""
+"""Read/write support for Maildir, mbox, MH, Babyl, and MMDF mailboxes."""
 
-
-import rfc822
 import os
+import time
+import calendar
+import socket
+import errno
+import copy
+import email
+import email.Message
+import email.Generator
+import rfc822
+import StringIO
+try:
+    import fnctl
+except ImportError:
+    fcntl = None
 
-__all__ = ["UnixMailbox","MmdfMailbox","MHMailbox","Maildir","BabylMailbox",
-           "PortableUnixMailbox"]
+__all__ = [ 'Mailbox', 'Maildir', 'mbox', 'MH', 'Babyl', 'MMDF',
+            'Message', 'MaildirMessage', 'mboxMessage', 'MHMessage',
+            'BabylMessage', 'MMDFMessage', 'UnixMailbox',
+            'PortableUnixMailbox', 'MmdfMailbox', 'MHMailbox', 'BabylMailbox' ]
 
-class _Mailbox:
 
-    def __init__(self, fp, factory=rfc822.Message):
-        self.fp = fp
-        self.seekp = 0
-        self.factory = factory
+class Mailbox:
+    """A group of messages in a particular place."""
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize a Mailbox instance."""
+        self._path = os.path.abspath(os.path.expanduser(path))
+        self._factory = factory
+
+    def add(self, message):
+        """Add message and return assigned key."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def remove(self, key):
+        """Remove the keyed message; raise KeyError if it doesn't exist."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def __delitem__(self, key):
+        self.remove(key)
+
+    def discard(self, key):
+        """If the keyed message exists, remove it."""
+        try:
+            self.remove(key)
+        except KeyError:
+            pass
+
+    def __setitem__(self, key, message):
+        """Replace the keyed message; raise KeyError if it doesn't exist."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def get(self, key, default=None):
+        """Return the keyed message, or default if it doesn't exist."""
+        try:
+            return self.__getitem__(key)
+        except KeyError:
+            return default
+
+    def __getitem__(self, key):
+        """Return the keyed message; raise KeyError if it doesn't exist."""
+        if not self._factory:
+            return self.get_message(key)
+        else:
+            return self._factory(self.get_file(key))
+
+    def get_message(self, key):
+        """Return a Message representation or raise a KeyError."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def get_string(self, key):
+        """Return a string representation or raise a KeyError."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def get_file(self, key):
+        """Return a file-like representation or raise a KeyError."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def iterkeys(self):
+        """Return an iterator over keys."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def keys(self):
+        """Return a list of keys."""
+        return list(self.iterkeys())
+
+    def itervalues(self):
+        """Return an iterator over all messages."""
+        for key in self.iterkeys():
+            try:
+                value = self[key]
+            except KeyError:
+                continue
+            yield value
 
     def __iter__(self):
-        return iter(self.next, None)
+        return self.itervalues()
 
+    def values(self):
+        """Return a list of messages. Memory intensive."""
+        return list(self.itervalues())
+
+    def iteritems(self):
+        """Return an iterator over (key, message) tuples."""
+        for key in self.iterkeys():
+            try:
+                value = self[key]
+            except KeyError:
+                continue
+            yield (key, value)
+
+    def items(self):
+        """Return a list of (key, message) tuples. Memory intensive."""
+        return list(self.iteritems())
+
+    def has_key(self, key):
+        """Return True if the keyed message exists, False otherwise."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def __contains__(self, key):
+        return self.has_key(key)
+
+    def __len__(self):
+        """Return a count of messages in the mailbox."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def clear(self):
+        """Delete all messages."""
+        for key in self.iterkeys():
+            self.discard(key)
+
+    def pop(self, key, default=None):
+        """Delete the keyed message and return it, or default."""
+        try:
+            result = self[key]
+        except KeyError:
+            return default
+        self.discard(key)
+        return result
+
+    def popitem(self):
+        """Delete an arbitrary (key, message) pair and return it."""
+        for key in self.iterkeys():
+            return (key, self.pop(key))     # This is only run once.
+        else:
+            raise KeyError('No messages in mailbox')
+
+    def update(self, arg=None):
+        """Change the messages that correspond to certain keys."""
+        if hasattr(arg, 'iteritems'):
+            source = arg.iteritems()
+        elif hasattr(arg, 'items'):
+            source = arg.items()
+        else:
+            source = arg
+        bad_key = False
+        for key, message in source:
+            try:
+                self[key] = message
+            except KeyError:
+                bad_key = True
+        if bad_key:
+            raise KeyError('No message with key(s)')
+
+    def flush(self):
+        """Write any pending changes to the disk."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def lock(self):
+        """Lock the mailbox."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def unlock(self):
+        """Unlock the mailbox if it is locked."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def close(self):
+        """Flush and close the mailbox."""
+        raise NotImplementedError('Method must be implemented by subclass')
+
+    def _dump_message(self, message, target, mangle_from_=False):
+        # Most files are opened in binary mode to allow predictable seeking.
+        # To get native line endings on disk, the user-friendly \n line endings
+        # used in strings and by email.Message are translated here.
+        """Dump message contents to target file."""
+        if isinstance(message, email.Message.Message):
+            buffer = StringIO.StringIO()
+            gen = email.Generator.Generator(buffer, mangle_from_, 0)
+            gen.flatten(message)
+            buffer.seek(0)
+            target.write(buffer.read().replace('\n', os.linesep))
+        elif isinstance(message, str):
+            if mangle_from_:
+                message = message.replace('\nFrom ', '\n>From ')
+            message = message.replace('\n', os.linesep)
+            target.write(message)
+        elif hasattr(message, 'read'):
+            while True:
+                line = message.readline()
+                if line == '':
+                    break
+                if mangle_from_ and line.startswith('From '):
+                    line = '>From ' + line[5:]
+                line = line.replace('\n', os.linesep)
+                target.write(line)
+        else:
+            raise TypeError('Invalid message type: %s' % type(message))
+
+
+class Maildir(Mailbox):
+    """A qmail-style Maildir mailbox."""
+
+    colon = ':'
+
+    def __init__(self, dirname, factory=rfc822.Message, create=True):
+        """Initialize a Maildir instance."""
+        Mailbox.__init__(self, dirname, factory, create)
+        if not os.path.exists(self._path):
+            if create:
+                os.mkdir(self._path, 0700)
+                os.mkdir(os.path.join(self._path, 'tmp'), 0700)
+                os.mkdir(os.path.join(self._path, 'new'), 0700)
+                os.mkdir(os.path.join(self._path, 'cur'), 0700)
+            else:
+                raise NoSuchMailboxError(self._path)
+        self._toc = {}
+
+    def add(self, message):
+        """Add message and return assigned key."""
+        tmp_file = self._create_tmp()
+        try:
+            self._dump_message(message, tmp_file)
+        finally:
+            tmp_file.close()
+        if isinstance(message, MaildirMessage):
+            subdir = message.get_subdir()
+            suffix = self.colon + message.get_info()
+            if suffix == self.colon:
+                suffix = ''
+        else:
+            subdir = 'new'
+            suffix = ''
+        uniq = os.path.basename(tmp_file.name).split(self.colon)[0]
+        dest = os.path.join(self._path, subdir, uniq + suffix)
+        os.rename(tmp_file.name, dest)
+        if isinstance(message, MaildirMessage):
+            os.utime(dest, (os.path.getatime(dest), message.get_date()))
+        return uniq
+
+    def remove(self, key):
+        """Remove the keyed message; raise KeyError if it doesn't exist."""
+        os.remove(os.path.join(self._path, self._lookup(key)))
+
+    def discard(self, key):
+        """If the keyed message exists, remove it."""
+        # This overrides an inapplicable implementation in the superclass.
+        try:
+            self.remove(key)
+        except KeyError:
+            pass
+        except OSError, e:
+            if e.errno == errno.ENOENT:
+                pass
+            else:
+                raise 
+
+    def __setitem__(self, key, message):
+        """Replace the keyed message; raise KeyError if it doesn't exist."""
+        old_subpath = self._lookup(key)
+        temp_key = self.add(message)
+        temp_subpath = self._lookup(temp_key)
+        if isinstance(message, MaildirMessage):
+            # temp's subdir and suffix were specified by message.
+            dominant_subpath = temp_subpath
+        else:
+            # temp's subdir and suffix were defaults from add().
+            dominant_subpath = old_subpath
+        subdir = os.path.dirname(dominant_subpath)
+        if self.colon in dominant_subpath:
+            suffix = self.colon + dominant_subpath.split(self.colon)[-1]
+        else:
+            suffix = ''
+        self.discard(key)
+        new_path = os.path.join(self._path, subdir, key + suffix)
+        os.rename(os.path.join(self._path, temp_subpath), new_path)
+        if isinstance(message, MaildirMessage):
+            os.utime(new_path, (os.path.getatime(new_path),
+                                message.get_date()))
+
+    def get_message(self, key):
+        """Return a Message representation or raise a KeyError."""
+        subpath = self._lookup(key)
+        f = file(os.path.join(self._path, subpath), 'r')
+        try:
+            msg = MaildirMessage(f)
+        finally:
+            f.close()
+        subdir, name = os.path.split(subpath)
+        msg.set_subdir(subdir)
+        if self.colon in name:
+            msg.set_info(name.split(self.colon)[-1])
+        msg.set_date(os.path.getmtime(os.path.join(self._path, subpath)))
+        return msg
+
+    def get_string(self, key):
+        """Return a string representation or raise a KeyError."""
+        f = file(os.path.join(self._path, self._lookup(key)), 'r')
+        try:
+            return f.read()
+        finally:
+            f.close()
+
+    def get_file(self, key):
+        """Return a file-like representation or raise a KeyError."""
+        f = file(os.path.join(self._path, self._lookup(key)), 'rb')
+        return _ProxyFile(f)
+
+    def iterkeys(self):
+        """Return an iterator over keys."""
+        self._refresh()
+        for key in self._toc:
+            try:
+                self._lookup(key)
+            except KeyError:
+                continue
+            yield key
+
+    def has_key(self, key):
+        """Return True if the keyed message exists, False otherwise."""
+        self._refresh()
+        return key in self._toc
+
+    def __len__(self):
+        """Return a count of messages in the mailbox."""
+        self._refresh()
+        return len(self._toc)
+
+    def flush(self):
+        """Write any pending changes to disk."""
+        return  # Maildir changes are always written immediately.
+
+    def lock(self):
+        """Lock the mailbox."""
+        return
+
+    def unlock(self):
+        """Unlock the mailbox if it is locked."""
+        return
+
+    def close(self):
+        """Flush and close the mailbox."""
+        return
+
+    def list_folders(self):
+        """Return a list of folder names."""
+        result = []
+        for entry in os.listdir(self._path):
+            if len(entry) > 1 and entry[0] == '.' and \
+               os.path.isdir(os.path.join(self._path, entry)):
+                result.append(entry[1:])
+        return result
+
+    def get_folder(self, folder):
+        """Return a Maildir instance for the named folder."""
+        return Maildir(os.path.join(self._path, '.' + folder), create=False)
+
+    def add_folder(self, folder):
+        """Create a folder and return a Maildir instance representing it."""
+        path = os.path.join(self._path, '.' + folder)
+        result = Maildir(path)
+        maildirfolder_path = os.path.join(path, 'maildirfolder')
+        if not os.path.exists(maildirfolder_path):
+            os.close(os.open(maildirfolder_path, os.O_CREAT | os.O_WRONLY))
+        return result
+
+    def remove_folder(self, folder):
+        """Delete the named folder, which must be empty."""
+        path = os.path.join(self._path, '.' + folder)
+        for entry in os.listdir(os.path.join(path, 'new')) + \
+                     os.listdir(os.path.join(path, 'cur')):
+            if len(entry) < 1 or entry[0] != '.':
+                raise NotEmptyError('Folder contains message(s): %s' % folder)
+        for entry in os.listdir(path):
+            if entry != 'new' and entry != 'cur' and entry != 'tmp' and \
+               os.path.isdir(os.path.join(path, entry)):
+                raise NotEmptyError("Folder contains subdirectory '%s': %s" %
+                                    (folder, entry))
+        for root, dirs, files in os.walk(path, topdown=False):
+            for entry in files:
+                os.remove(os.path.join(root, entry))
+            for entry in dirs:
+                os.rmdir(os.path.join(root, entry))
+        os.rmdir(path)
+
+    def clean(self):
+        """Delete old files in "tmp"."""
+        now = time.time()
+        for entry in os.listdir(os.path.join(self._path, 'tmp')):
+            path = os.path.join(self._path, 'tmp', entry)
+            if now - os.path.getatime(path) > 129600:   # 60 * 60 * 36
+                os.remove(path)
+
+    _count = 1  # This is used to generate unique file names.
+
+    def _create_tmp(self):
+        """Create a file in the tmp subdirectory and open and return it."""
+        now = time.time()
+        hostname = socket.gethostname()
+        if '/' in hostname:
+            hostname = hostname.replace('/', r'\057')
+        if ':' in hostname:
+            hostname = hostname.replace(':', r'\072')
+        uniq = "%s.M%sP%sQ%s.%s" % (int(now), int(now % 1 * 1e6), os.getpid(),
+                                    Maildir._count, hostname)
+        path = os.path.join(self._path, 'tmp', uniq)
+        try:
+            os.stat(path)
+        except OSError, e:
+            if e.errno == errno.ENOENT:
+                Maildir._count += 1
+                return file(path, 'wb+')
+            else:
+                raise
+        else:
+            raise ExternalClashError('Name clash prevented file creation: %s' %
+                                     path)
+
+    def _refresh(self):
+        """Update table of contents mapping."""
+        self._toc = {}
+        for subdir in ('new', 'cur'):
+            for entry in os.listdir(os.path.join(self._path, subdir)):
+                uniq = entry.split(self.colon)[0]
+                self._toc[uniq] = os.path.join(subdir, entry)
+
+    def _lookup(self, key):
+        """Use TOC to return subpath for given key, or raise a KeyError."""
+        try:
+            if os.path.exists(os.path.join(self._path, self._toc[key])):
+                return self._toc[key]
+        except KeyError:
+            pass
+        self._refresh()
+        try:
+            return self._toc[key]
+        except KeyError:
+            raise KeyError('No message with key: %s' % key)
+
+    # This method is for backward compatibility only.
     def next(self):
-        while 1:
-            self.fp.seek(self.seekp)
+        """Return the next message in a one-time iteration."""
+        if not hasattr(self, '_onetime_keys'):
+            self._onetime_keys = self.iterkeys()
+        while True:
             try:
-                self._search_start()
-            except EOFError:
-                self.seekp = self.fp.tell()
+                return self[self._onetime_keys.next()]
+            except StopIteration:
                 return None
-            start = self.fp.tell()
-            self._search_end()
-            self.seekp = stop = self.fp.tell()
-            if start != stop:
+            except KeyError:
+                continue
+
+
+class _singlefileMailbox(Mailbox):
+    """A single-file mailbox."""
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize a single-file mailbox."""
+        Mailbox.__init__(self, path, factory, create)
+        try:
+            f = file(self._path, 'rb+')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                if create:
+                    f = file(self._path, 'wb+')
+                else:
+                    raise NoSuchMailboxError(self._path)
+            elif e.errno == errno.EACCES:
+                f = file(self._path, 'rb')
+            else:
+                raise
+        self._file = f
+        self._toc = None
+        self._next_key = 0
+        self._pending = False   # No changes require rewriting the file.
+        self._locked = False
+
+    def add(self, message):
+        """Add message and return assigned key."""
+        self._lookup()
+        self._toc[self._next_key] = self._append_message(message)
+        self._next_key += 1
+        self._pending = True
+        return self._next_key - 1
+
+    def remove(self, key):
+        """Remove the keyed message; raise KeyError if it doesn't exist."""
+        self._lookup(key)
+        del self._toc[key]
+        self._pending = True
+
+    def __setitem__(self, key, message):
+        """Replace the keyed message; raise KeyError if it doesn't exist."""
+        self._lookup(key)
+        self._toc[key] = self._append_message(message)
+        self._pending = True
+
+    def iterkeys(self):
+        """Return an iterator over keys."""
+        self._lookup()
+        for key in self._toc.keys():
+            yield key
+
+    def has_key(self, key):
+        """Return True if the keyed message exists, False otherwise."""
+        self._lookup()
+        return key in self._toc
+
+    def __len__(self):
+        """Return a count of messages in the mailbox."""
+        self._lookup()
+        return len(self._toc)
+
+    def lock(self):
+        """Lock the mailbox."""
+        if not self._locked:
+            _lock_file(self._file)
+            self._locked = True
+
+    def unlock(self):
+        """Unlock the mailbox if it is locked."""
+        if self._locked:
+            _unlock_file(self._file)
+            self._locked = False
+
+    def flush(self):
+        """Write any pending changes to disk."""
+        if not self._pending:
+            return
+        self._lookup()
+        new_file = _create_temporary(self._path)
+        try:
+            new_toc = {}
+            self._pre_mailbox_hook(new_file)
+            for key in sorted(self._toc.keys()):
+                start, stop = self._toc[key]
+                self._file.seek(start)
+                self._pre_message_hook(new_file)
+                new_start = new_file.tell()
+                while True:
+                    buffer = self._file.read(min(4096,
+                                                 stop - self._file.tell()))
+                    if buffer == '':
                         break
-        return self.factory(_Subfile(self.fp, start, stop))
+                    new_file.write(buffer)
+                new_toc[key] = (new_start, new_file.tell())
+                self._post_message_hook(new_file)
+        except:
+            new_file.close()
+            os.remove(new_file.name)
+            raise
+        new_file.close()
+        self._file.close()
+        try:
+            os.rename(new_file.name, self._path)
+        except OSError, e:
+            if e.errno == errno.EEXIST:
+                os.remove(self._path)
+                os.rename(new_file.name, self._path)
+            else:
+                raise
+        self._file = file(self._path, 'rb+')
+        self._toc = new_toc
+        self._pending = False
+        if self._locked:
+            _lock_file(new_file, dotlock=False)
 
+    def _pre_mailbox_hook(self, f):
+        """Called before writing the mailbox to file f."""
+        return
 
-class _Subfile:
+    def _pre_message_hook(self, f):
+        """Called before writing each message to file f."""
+        return
 
-    def __init__(self, fp, start, stop):
-        self.fp = fp
-        self.start = start
-        self.stop = stop
-        self.pos = self.start
+    def _post_message_hook(self, f):
+        """Called after writing each message to file f."""
+        return
 
+    def close(self):
+        """Flush and close the mailbox."""
+        self.flush()
+        if self._locked:
+            self.unlock()
+        self._file.close()
 
-    def _read(self, length, read_function):
-        if self.pos >= self.stop:
-            return ''
-        remaining = self.stop - self.pos
-        if length is None or length < 0 or length > remaining:
-            length = remaining
-        self.fp.seek(self.pos)
-        data = read_function(length)
-        self.pos = self.fp.tell()
-        return data
-
-    def read(self, length = None):
-        return self._read(length, self.fp.read)
-
-    def readline(self, length = None):
-        return self._read(length, self.fp.readline)
-
-    def readlines(self, sizehint = -1):
-        lines = []
-        while 1:
-            line = self.readline()
-            if not line:
+    def _lookup(self, key=None):
+        """Return (start, stop) or raise KeyError."""
+        if self._toc is None:
+            self._generate_toc()
+        if key is not None:
+            try:
+                return self._toc[key]
+            except KeyError:
+                raise KeyError('No message with key: %s' % key)
+
+    def _append_message(self, message):
+        """Append message to mailbox and return (start, stop) offsets."""
+        self._file.seek(0, 2)
+        self._pre_message_hook(self._file)
+        offsets = self._install_message(message)
+        self._post_message_hook(self._file)
+        self._file.flush()
+        return offsets
+
+
+
+class _mboxMMDF(_singlefileMailbox):
+    """An mbox or MMDF mailbox."""
+
+    _mangle_from_ = True
+
+    def get_message(self, key):
+        """Return a Message representation or raise a KeyError."""
+        start, stop = self._lookup(key)
+        self._file.seek(start)
+        from_line = self._file.readline().replace(os.linesep, '')
+        string = self._file.read(stop - self._file.tell())
+        msg = self._message_factory(string.replace(os.linesep, '\n'))
+        msg.set_from(from_line[5:])
+        return msg
+
+    def get_string(self, key, from_=False):
+        """Return a string representation or raise a KeyError."""
+        start, stop = self._lookup(key)
+        self._file.seek(start)
+        if not from_:
+            self._file.readline()
+        string = self._file.read(stop - self._file.tell())
+        return string.replace(os.linesep, '\n')
+
+    def get_file(self, key, from_=False):
+        """Return a file-like representation or raise a KeyError."""
+        start, stop = self._lookup(key)
+        self._file.seek(start)
+        if not from_:
+            self._file.readline()
+        return _PartialFile(self._file, self._file.tell(), stop)
+
+    def _install_message(self, message):
+        """Format a message and blindly write to self._file."""
+        from_line = None
+        if isinstance(message, str) and message.startswith('From '):
+            newline = message.find('\n')
+            if newline != -1:
+                from_line = message[:newline]
+                message = message[newline + 1:]
+            else:
+                from_line = message
+                message = ''
+        elif isinstance(message, _mboxMMDFMessage):
+            from_line = 'From ' + message.get_from()
+        elif isinstance(message, email.Message.Message):
+            from_line = message.get_unixfrom()  # May be None.
+        if from_line is None:
+            from_line = 'From MAILER-DAEMON %s' % time.asctime(time.gmtime())
+        start = self._file.tell()
+        self._file.write(from_line + os.linesep)
+        self._dump_message(message, self._file, self._mangle_from_)
+        stop = self._file.tell()
+        return (start, stop)
+
+
+class mbox(_mboxMMDF):
+    """A classic mbox mailbox."""
+
+    _mangle_from_ = True
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize an mbox mailbox."""
+        self._message_factory = mboxMessage
+        _mboxMMDF.__init__(self, path, factory, create)
+
+    def _pre_message_hook(self, f):
+        """Called before writing each message to file f."""
+        if f.tell() != 0:
+            f.write(os.linesep)
+
+    def _generate_toc(self):
+        """Generate key-to-(start, stop) table of contents."""
+        starts, stops = [], []
+        self._file.seek(0)
+        while True:
+            line_pos = self._file.tell()
+            line = self._file.readline()
+            if line.startswith('From '):
+                if len(stops) < len(starts):
+                    stops.append(line_pos - len(os.linesep))
+                starts.append(line_pos)
+            elif line == '':
+                stops.append(line_pos)
+                break
+        self._toc = dict(enumerate(zip(starts, stops)))
+        self._next_key = len(self._toc)
+
+
+class MMDF(_mboxMMDF):
+    """An MMDF mailbox."""
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize an MMDF mailbox."""
+        self._message_factory = MMDFMessage
+        _mboxMMDF.__init__(self, path, factory, create)
+
+    def _pre_message_hook(self, f):
+        """Called before writing each message to file f."""
+        f.write('\001\001\001\001' + os.linesep)
+
+    def _post_message_hook(self, f):
+        """Called after writing each message to file f."""
+        f.write(os.linesep + '\001\001\001\001' + os.linesep)
+
+    def _generate_toc(self):
+        """Generate key-to-(start, stop) table of contents."""
+        starts, stops = [], []
+        self._file.seek(0)
+        next_pos = 0
+        while True:
+            line_pos = next_pos
+            line = self._file.readline()
+            next_pos = self._file.tell()
+            if line.startswith('\001\001\001\001' + os.linesep):
+                starts.append(next_pos)
+                while True:
+                    line_pos = next_pos
+                    line = self._file.readline()
+                    next_pos = self._file.tell()
+                    if line == '\001\001\001\001' + os.linesep:
+                        stops.append(line_pos - len(os.linesep))
+                        break
+                    elif line == '':
+                        stops.append(line_pos)
                         break
-            lines.append(line)
-            if sizehint >= 0:
-                sizehint = sizehint - len(line)
+            elif line == '':
+                break
+        self._toc = dict(enumerate(zip(starts, stops)))
+        self._next_key = len(self._toc)
+
+
+class MH(Mailbox):
+    """An MH mailbox."""
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize an MH instance."""
+        Mailbox.__init__(self, path, factory, create)
+        if not os.path.exists(self._path):
+            if create:
+                os.mkdir(self._path, 0700)
+                os.close(os.open(os.path.join(self._path, '.mh_sequences'),
+                                 os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0600))
+            else:
+                raise NoSuchMailboxError(self._path)
+        self._locked = False
+
+    def add(self, message):
+        """Add message and return assigned key."""
+        keys = self.keys()
+        if len(keys) == 0:
+            new_key = 1
+        else:
+            new_key = max(keys) + 1
+        new_path = os.path.join(self._path, str(new_key))
+        f = _create_carefully(new_path)
+        try:
+            if self._locked:
+                _lock_file(f)
+            try:
+                self._dump_message(message, f)
+                if isinstance(message, MHMessage):
+                    self._dump_sequences(message, new_key)
+            finally:
+                if self._locked:
+                    _unlock_file(f)
+        finally:
+            f.close()
+        return new_key
+
+    def remove(self, key):
+        """Remove the keyed message; raise KeyError if it doesn't exist."""
+        path = os.path.join(self._path, str(key))
+        try:
+            f = file(path, 'rb+')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                raise KeyError('No message with key: %s' % key)
+            else:
+                raise
+        try:
+            if self._locked:
+                _lock_file(f)
+            try:
+                f.close()
+                os.remove(os.path.join(self._path, str(key)))
+            finally:
+                if self._locked:
+                    _unlock_file(f)
+        finally:
+            f.close()
+
+    def __setitem__(self, key, message):
+        """Replace the keyed message; raise KeyError if it doesn't exist."""
+        path = os.path.join(self._path, str(key))
+        try:
+            f = file(path, 'rb+')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                raise KeyError('No message with key: %s' % key)
+            else:
+                raise
+        try:
+            if self._locked:
+                _lock_file(f)
+            try:
+                os.close(os.open(path, os.O_WRONLY | os.O_TRUNC))
+                self._dump_message(message, f)
+                if isinstance(message, MHMessage):
+                    self._dump_sequences(message, key)
+            finally:
+                if self._locked:
+                    _unlock_file(f)
+        finally:
+            f.close()
+
+    def get_message(self, key):
+        """Return a Message representation or raise a KeyError."""
+        try:
+            if self._locked:
+                f = file(os.path.join(self._path, str(key)), 'r+')
+            else:
+                f = file(os.path.join(self._path, str(key)), 'r')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                raise KeyError('No message with key: %s' % key)
+            else:
+                raise
+        try:
+            if self._locked:
+                _lock_file(f)
+            try:
+                msg = MHMessage(f)
+            finally:
+                if self._locked:
+                    _unlock_file(f)
+        finally:
+            f.close()
+        for name, key_list in self.get_sequences():
+            if key in key_list:
+                msg.add_sequence(name)
+        return msg
+
+    def get_string(self, key):
+        """Return a string representation or raise a KeyError."""
+        try:
+            if self._locked:
+                f = file(os.path.join(self._path, str(key)), 'r+')
+            else:
+                f = file(os.path.join(self._path, str(key)), 'r')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                raise KeyError('No message with key: %s' % key)
+            else:
+                raise
+        try:
+            if self._locked:
+                _lock_file(f)
+            try:
+                return f.read()
+            finally:
+                if self._locked:
+                    _unlock_file(f)
+        finally:
+            f.close()
+
+    def get_file(self, key):
+        """Return a file-like representation or raise a KeyError."""
+        try:
+            f = file(os.path.join(self._path, str(key)), 'rb')
+        except IOError, e:
+            if e.errno == errno.ENOENT:
+                raise KeyError('No message with key: %s' % key)
+            else:
+                raise
+        return _ProxyFile(f)
+
+    def iterkeys(self):
+        """Return an iterator over keys."""
+        return iter(sorted(int(entry) for entry in os.listdir(self._path)
+                                      if entry.isdigit()))
+
+    def has_key(self, key):
+        """Return True if the keyed message exists, False otherwise."""
+        return os.path.exists(os.path.join(self._path, str(key)))
+
+    def __len__(self):
+        """Return a count of messages in the mailbox."""
+        return len(list(self.iterkeys()))
+
+    def lock(self):
+        """Lock the mailbox."""
+        if not self._locked:
+            self._file = file(os.path.join(self._path, '.mh_sequences'), 'rb+')
+            _lock_file(self._file)
+            self._locked = True
+
+    def unlock(self):
+        """Unlock the mailbox if it is locked."""
+        if self._locked:
+            _unlock_file(self._file)
+            self._file.close()
+            del self._file
+            self._locked = False
+
+    def flush(self):
+        """Write any pending changes to the disk."""
+        return
+
+    def close(self):
+        """Flush and close the mailbox."""
+        if self._locked:
+            self.unlock()
+
+    def list_folders(self):
+        """Return a list of folder names."""
+        result = []
+        for entry in os.listdir(self._path):
+            if os.path.isdir(os.path.join(self._path, entry)):
+                result.append(entry)
+        return result
+
+    def get_folder(self, folder):
+        """Return an MH instance for the named folder."""
+        return MH(os.path.join(self._path, folder), create=False)
+
+    def add_folder(self, folder):
+        """Create a folder and return an MH instance representing it."""
+        return MH(os.path.join(self._path, folder))
+
+    def remove_folder(self, folder):
+        """Delete the named folder, which must be empty."""
+        path = os.path.join(self._path, folder)
+        entries = os.listdir(path)
+        if entries == ['.mh_sequences']:
+            os.remove(os.path.join(path, '.mh_sequences'))
+        elif entries == []:
+            pass
+        else:
+            raise NotEmptyError('Folder not empty: %s' % self._path)
+        os.rmdir(path)
+
+    def get_sequences(self):
+        """Return a name-to-key-list dictionary to define each sequence."""
+        results = {}
+        f = file(os.path.join(self._path, '.mh_sequences'), 'r')
+        try:
+            all_keys = set(self.keys())
+            for line in f:
+                try:
+                    name, contents = line.split(':')
+                    keys = set()
+                    for spec in contents.split():
+                        if spec.isdigit():
+                            keys.add(int(spec))
+                        else:
+                            start, stop = (int(x) for x in spec.split('-'))
+                            keys.update(range(start, stop + 1))
+                    results[name] = [key for key in sorted(keys) \
+                                         if key in all_keys]
+                    if len(results[name]) == 0:
+                        del results[name]
+                except ValueError:
+                    raise FormatError('Invalid sequence specification: %s' %
+                                      line.rstrip())
+        finally:
+            f.close()
+        return results
+
+    def set_sequences(self, sequences):
+        """Set sequences using the given name-to-key-list dictionary."""
+        f = file(os.path.join(self._path, '.mh_sequences'), 'r+')
+        try:
+            os.close(os.open(f.name, os.O_WRONLY | os.O_TRUNC))
+            for name, keys in sequences.iteritems():
+                if len(keys) == 0:
+                    continue
+                f.write('%s:' % name)
+                prev = None
+                completing = False
+                for key in sorted(set(keys)):
+                    if key - 1 == prev:
+                        if not completing:
+                            completing = True
+                            f.write('-')
+                    elif completing:
+                        completing = False
+                        f.write('%s %s' % (prev, key))
+                    else:
+                        f.write(' %s' % key)
+                    prev = key
+                if completing:
+                    f.write(str(prev) + '\n')
+                else:
+                    f.write('\n')
+        finally:
+            f.close()
+
+    def pack(self):
+        """Re-name messages to eliminate numbering gaps. Invalidates keys."""
+        sequences = self.get_sequences()
+        prev = 0
+        changes = []
+        for key in self.iterkeys():
+            if key - 1 != prev:
+                changes.append((key, prev + 1))
+                f = file(os.path.join(self._path, str(key)), 'r+')
+                try:
+                    if self._locked:
+                        _lock_file(f)
+                    try:
+                        if hasattr(os, 'link'):
+                            os.link(os.path.join(self._path, str(key)),
+                                    os.path.join(self._path, str(prev + 1)))
+                            os.unlink(os.path.join(self._path, str(key)))
+                        else:
+                            f.close()
+                            os.rename(os.path.join(self._path, str(key)),
+                                      os.path.join(self._path, str(prev + 1)))
+                    finally:
+                        if self._locked:
+                            _unlock_file(f)
+                finally:
+                    f.close()
+            prev += 1
+        self._next_key = prev + 1
+        if len(changes) == 0:
+            return
+        for name, key_list in sequences.items():
+            for old, new in changes:
+                if old in key_list:
+                    key_list[key_list.index(old)] = new
+        self.set_sequences(sequences)
+
+    def _dump_sequences(self, message, key):
+        """Inspect a new MHMessage and update sequences appropriately."""
+        pending_sequences = message.get_sequences()
+        all_sequences = self.get_sequences()
+        for name, key_list in all_sequences.iteritems():
+            if name in pending_sequences:
+                key_list.append(key)
+            elif key in key_list:
+                del key_list[key_list.index(key)]
+        for sequence in pending_sequences:
+            if sequence not in all_sequences:
+                all_sequences[sequence] = [key]
+        self.set_sequences(all_sequences)
+
+
+class Babyl(_singlefileMailbox):
+    """An Rmail-style Babyl mailbox."""
+
+    _special_labels = frozenset(('unseen', 'deleted', 'filed', 'answered',
+                                 'forwarded', 'edited', 'resent'))
+
+    def __init__(self, path, factory=None, create=True):
+        """Initialize a Babyl mailbox."""
+        _singlefileMailbox.__init__(self, path, factory, create)
+        self._labels = {}
+
+    def add(self, message):
+        """Add message and return assigned key."""
+        key = _singlefileMailbox.add(self, message)
+        if isinstance(message, BabylMessage):
+            self._labels[key] = message.get_labels()
+        return key
+
+    def remove(self, key):
+        """Remove the keyed message; raise KeyError if it doesn't exist."""
+        _singlefileMailbox.remove(self, key)
+        if key in self._labels:
+            del self._labels[key]
+
+    def __setitem__(self, key, message):
+        """Replace the keyed message; raise KeyError if it doesn't exist."""
+        _singlefileMailbox.__setitem__(self, key, message)
+        if isinstance(message, BabylMessage):
+            self._labels[key] = message.get_labels()
+
+    def get_message(self, key):
+        """Return a Message representation or raise a KeyError."""
+        start, stop = self._lookup(key)
+        self._file.seek(start)
+        self._file.readline()   # Skip '1,' line specifying labels.
+        original_headers = StringIO.StringIO()
+        while True:
+            line = self._file.readline()
+            if line == '*** EOOH ***' + os.linesep or line == '':
+                break
+            original_headers.write(line.replace(os.linesep, '\n'))
+        visible_headers = StringIO.StringIO()
+        while True:
+            line = self._file.readline()
+            if line == os.linesep or line == '':
+                break
+            visible_headers.write(line.replace(os.linesep, '\n'))
+        body = self._file.read(stop - self._file.tell()).replace(os.linesep,
+                                                                 '\n')
+        msg = BabylMessage(original_headers.getvalue() + body)
+        msg.set_visible(visible_headers.getvalue())
+        if key in self._labels:
+            msg.set_labels(self._labels[key])
+        return msg
+
+    def get_string(self, key):
+        """Return a string representation or raise a KeyError."""
+        start, stop = self._lookup(key)
+        self._file.seek(start)
+        self._file.readline()   # Skip '1,' line specifying labels.
+        original_headers = StringIO.StringIO()
+        while True:
+            line = self._file.readline()
+            if line == '*** EOOH ***' + os.linesep or line == '':
+                break
+            original_headers.write(line.replace(os.linesep, '\n'))
+        while True:
+            line = self._file.readline()
+            if line == os.linesep or line == '':
+                break
+        return original_headers.getvalue() + \
+               self._file.read(stop - self._file.tell()).replace(os.linesep,
+                                                                 '\n')
+
+    def get_file(self, key):
+        """Return a file-like representation or raise a KeyError."""
+        return StringIO.StringIO(self.get_string(key).replace('\n',
+                                                              os.linesep))
+
+    def get_labels(self):
+        """Return a list of user-defined labels in the mailbox."""
+        self._lookup()
+        labels = set()
+        for label_list in self._labels.values():
+            labels.update(label_list)
+        labels.difference_update(self._special_labels)
+        return list(labels)
+
+    def _generate_toc(self):
+        """Generate key-to-(start, stop) table of contents."""
+        starts, stops = [], []
+        self._file.seek(0)
+        next_pos = 0
+        label_lists = []
+        while True:
+            line_pos = next_pos
+            line = self._file.readline()
+            next_pos = self._file.tell()
+            if line == '\037\014' + os.linesep:
+                if len(stops) < len(starts):
+                    stops.append(line_pos - len(os.linesep))
+                starts.append(next_pos)
+                labels = [label.strip() for label
+                                        in self._file.readline()[1:].split(',')
+                                        if label.strip() != '']
+                label_lists.append(labels)
+            elif line == '\037' or line == '\037' + os.linesep:
+                if len(stops) < len(starts):
+                    stops.append(line_pos - len(os.linesep))
+            elif line == '':
+                stops.append(line_pos - len(os.linesep))
+                break
+        self._toc = dict(enumerate(zip(starts, stops)))
+        self._labels = dict(enumerate(label_lists))
+        self._next_key = len(self._toc)
+
+    def _pre_mailbox_hook(self, f):
+        """Called before writing the mailbox to file f."""
+        f.write('BABYL OPTIONS:%sVersion: 5%sLabels:%s%s\037' %
+                (os.linesep, os.linesep, ','.join(self.get_labels()),
+                 os.linesep))
+
+    def _pre_message_hook(self, f):
+        """Called before writing each message to file f."""
+        f.write('\014' + os.linesep)
+
+    def _post_message_hook(self, f):
+        """Called after writing each message to file f."""
+        f.write(os.linesep + '\037')
+
+    def _install_message(self, message):
+        """Write message contents and return (start, stop)."""
+        start = self._file.tell()
+        if isinstance(message, BabylMessage):
+            special_labels = []
+            labels = []
+            for label in message.get_labels():
+                if label in self._special_labels:
+                    special_labels.append(label)
+                else:
+                    labels.append(label)
+            self._file.write('1')
+            for label in special_labels:
+                self._file.write(', ' + label)
+            self._file.write(',,')
+            for label in labels:
+                self._file.write(' ' + label + ',')
+            self._file.write(os.linesep)
+        else:
+            self._file.write('1,,' + os.linesep)
+        if isinstance(message, email.Message.Message):
+            orig_buffer = StringIO.StringIO()
+            orig_generator = email.Generator.Generator(orig_buffer, False, 0)
+            orig_generator.flatten(message)
+            orig_buffer.seek(0)
+            while True:
+                line = orig_buffer.readline()
+                self._file.write(line.replace('\n', os.linesep))
+                if line == '\n' or line == '':
+                    break
+            self._file.write('*** EOOH ***' + os.linesep)
+            if isinstance(message, BabylMessage):
+                vis_buffer = StringIO.StringIO()
+                vis_generator = email.Generator.Generator(vis_buffer, False, 0)
+                vis_generator.flatten(message.get_visible())
+                while True:
+                    line = vis_buffer.readline()
+                    self._file.write(line.replace('\n', os.linesep))
+                    if line == '\n' or line == '':
+                        break
+            else:
+                orig_buffer.seek(0)
+                while True:
+                    line = orig_buffer.readline()
+                    self._file.write(line.replace('\n', os.linesep))
+                    if line == '\n' or line == '':
+                        break
+            while True:
+                buffer = orig_buffer.read(4096) # Buffer size is arbitrary.
+                if buffer == '':
+                    break
+                self._file.write(buffer.replace('\n', os.linesep))
+        elif isinstance(message, str):
+            body_start = message.find('\n\n') + 2
+            if body_start - 2 != -1:
+                self._file.write(message[:body_start].replace('\n',
+                                                              os.linesep))
+                self._file.write('*** EOOH ***' + os.linesep)
+                self._file.write(message[:body_start].replace('\n',
+                                                              os.linesep))
+                self._file.write(message[body_start:].replace('\n',
+                                                              os.linesep))
+            else:
+                self._file.write('*** EOOH ***' + os.linesep + os.linesep)
+                self._file.write(message.replace('\n', os.linesep))
+        elif hasattr(message, 'readline'):
+            original_pos = message.tell()
+            first_pass = True
+            while True:
+                line = message.readline()
+                self._file.write(line.replace('\n', os.linesep))
+                if line == '\n' or line == '':
+                    self._file.write('*** EOOH ***' + os.linesep)
+                    if first_pass:
+                        first_pass = False
+                        message.seek(original_pos)
+                    else:
+                        break
+            while True:
+                buffer = message.read(4096)     # Buffer size is arbitrary.
+                if buffer == '':
+                    break
+                self._file.write(buffer.replace('\n', os.linesep))
+        else:
+            raise TypeError('Invalid message type: %s' % type(message))
+        stop = self._file.tell()
+        return (start, stop)
+
+
+class Message(email.Message.Message):
+    """Message with mailbox-format-specific properties."""
+
+    def __init__(self, message=None):
+        """Initialize a Message instance."""
+        if isinstance(message, email.Message.Message):
+            self._become_message(copy.deepcopy(message))
+            if isinstance(message, Message):
+                message._explain_to(self)
+        elif isinstance(message, str):
+            self._become_message(email.message_from_string(message))
+        elif hasattr(message, "read"):
+            self._become_message(email.message_from_file(message))
+        elif message is None:
+            email.Message.Message.__init__(self)
+        else:
+            raise TypeError('Invalid message type: %s' % type(message))
+
+    def _become_message(self, message):
+        """Assume the non-format-specific state of message."""
+        for name in ('_headers', '_unixfrom', '_payload', '_charset',
+                     'preamble', 'epilogue', 'defects', '_default_type'):
+            self.__dict__[name] = message.__dict__[name]
+
+    def _explain_to(self, message):
+        """Copy format-specific state to message insofar as possible."""
+        if isinstance(message, Message):
+            return  # There's nothing format-specific to explain.
+        else:
+            raise TypeError('Cannot convert to specified type')
+
+
+class MaildirMessage(Message):
+    """Message with Maildir-specific properties."""
+
+    def __init__(self, message=None):
+        """Initialize a MaildirMessage instance."""
+        self._subdir = 'new'
+        self._info = ''
+        self._date = time.time()
+        Message.__init__(self, message)
+
+    def get_subdir(self):
+        """Return 'new' or 'cur'."""
+        return self._subdir
+
+    def set_subdir(self, subdir):
+        """Set subdir to 'new' or 'cur'."""
+        if subdir == 'new' or subdir == 'cur':
+            self._subdir = subdir
+        else:
+            raise ValueError("subdir must be 'new' or 'cur': %s" % subdir)
+
+    def get_flags(self):
+        """Return as a string the flags that are set."""
+        if self._info.startswith('2,'):
+            return self._info[2:]
+        else:
+            return ''
+
+    def set_flags(self, flags):
+        """Set the given flags and unset all others."""
+        self._info = '2,' + ''.join(sorted(flags))
+
+    def add_flag(self, flag):
+        """Set the given flag(s) without changing others."""
+        self.set_flags(''.join(set(self.get_flags()) | set(flag)))
+
+    def remove_flag(self, flag):
+        """Unset the given string flag(s) without changing others."""
+        if self.get_flags() != '':
+            self.set_flags(''.join(set(self.get_flags()) - set(flag)))
+
+    def get_date(self):
+        """Return delivery date of message, in seconds since the epoch."""
+        return self._date
+
+    def set_date(self, date):
+        """Set delivery date of message, in seconds since the epoch."""
+        try:
+            self._date = float(date)
+        except ValueError:
+            raise TypeError("can't convert to float: %s" % date)
+
+    def get_info(self):
+        """Get the message's "info" as a string."""
+        return self._info
+
+    def set_info(self, info):
+        """Set the message's "info" string."""
+        if isinstance(info, str):
+            self._info = info
+        else:
+            raise TypeError('info must be a string: %s' % type(info))
+
+    def _explain_to(self, message):
+        """Copy Maildir-specific state to message insofar as possible."""
+        if isinstance(message, MaildirMessage):
+            message.set_flags(self.get_flags())
+            message.set_subdir(self.get_subdir())
+            message.set_date(self.get_date())
+        elif isinstance(message, _mboxMMDFMessage):
+            flags = set(self.get_flags())
+            if 'S' in flags:
+                message.add_flag('R')
+            if self.get_subdir() == 'cur':
+                message.add_flag('O')
+            if 'T' in flags:
+                message.add_flag('D')
+            if 'F' in flags:
+                message.add_flag('F')
+            if 'R' in flags:
+                message.add_flag('A')
+            message.set_from('MAILER-DAEMON', time.gmtime(self.get_date()))
+        elif isinstance(message, MHMessage):
+            flags = set(self.get_flags())
+            if 'S' not in flags:
+                message.add_sequence('unseen')
+            if 'R' in flags:
+                message.add_sequence('replied')
+            if 'F' in flags:
+                message.add_sequence('flagged')
+        elif isinstance(message, BabylMessage):
+            flags = set(self.get_flags())
+            if 'S' not in flags:
+                message.add_label('unseen')
+            if 'T' in flags:
+                message.add_label('deleted')
+            if 'R' in flags:
+                message.add_label('answered')
+            if 'P' in flags:
+                message.add_label('forwarded')
+        elif isinstance(message, Message):
+            pass
+        else:
+            raise TypeError('Cannot convert to specified type: %s' %
+                            type(message))
+
+
+class _mboxMMDFMessage(Message):
+    """Message with mbox- or MMDF-specific properties."""
+
+    def __init__(self, message=None):
+        """Initialize an mboxMMDFMessage instance."""
+        self.set_from('MAILER-DAEMON', True)
+        if isinstance(message, email.Message.Message):
+            unixfrom = message.get_unixfrom()
+            if unixfrom is not None and unixfrom.startswith('From '):
+                self.set_from(unixfrom[5:])
+        Message.__init__(self, message)
+
+    def get_from(self):
+        """Return contents of "From " line."""
+        return self._from
+
+    def set_from(self, from_, time_=None):
+        """Set "From " line, formatting and appending time_ if specified."""
+        if time_ is not None:
+            if time_ is True:
+                time_ = time.gmtime()
+            from_ += ' ' + time.asctime(time_)
+        self._from = from_
+
+    def get_flags(self):
+        """Return as a string the flags that are set."""
+        return self.get('Status', '') + self.get('X-Status', '')
+
+    def set_flags(self, flags):
+        """Set the given flags and unset all others."""
+        flags = set(flags)
+        status_flags, xstatus_flags = '', ''
+        for flag in ('R', 'O'):
+            if flag in flags:
+                status_flags += flag
+                flags.remove(flag)
+        for flag in ('D', 'F', 'A'):
+            if flag in flags:
+                xstatus_flags += flag
+                flags.remove(flag)
+        xstatus_flags += ''.join(sorted(flags))
+        try:
+            self.replace_header('Status', status_flags)
+        except KeyError:
+            self.add_header('Status', status_flags)
+        try:
+            self.replace_header('X-Status', xstatus_flags)
+        except KeyError:
+            self.add_header('X-Status', xstatus_flags)
+
+    def add_flag(self, flag):
+        """Set the given flag(s) without changing others."""
+        self.set_flags(''.join(set(self.get_flags()) | set(flag)))
+
+    def remove_flag(self, flag):
+        """Unset the given string flag(s) without changing others."""
+        if 'Status' in self or 'X-Status' in self:
+            self.set_flags(''.join(set(self.get_flags()) - set(flag)))
+
+    def _explain_to(self, message):
+        """Copy mbox- or MMDF-specific state to message insofar as possible."""
+        if isinstance(message, MaildirMessage):
+            flags = set(self.get_flags())
+            if 'O' in flags:
+                message.set_subdir('cur')
+            if 'F' in flags:
+                message.add_flag('F')
+            if 'A' in flags:
+                message.add_flag('R')
+            if 'R' in flags:
+                message.add_flag('S')
+            if 'D' in flags:
+                message.add_flag('T')
+            del message['status']
+            del message['x-status']
+            maybe_date = ' '.join(self.get_from().split()[-5:])
+            try:
+                message.set_date(calendar.timegm(time.strptime(maybe_date,
+                                                      '%a %b %d %H:%M:%S %Y')))
+            except (ValueError, OverflowError):
+                pass
+        elif isinstance(message, _mboxMMDFMessage):
+            message.set_flags(self.get_flags())
+            message.set_from(self.get_from())
+        elif isinstance(message, MHMessage):
+            flags = set(self.get_flags())
+            if 'R' not in flags:
+                message.add_sequence('unseen')
+            if 'A' in flags:
+                message.add_sequence('replied')
+            if 'F' in flags:
+                message.add_sequence('flagged')
+            del message['status']
+            del message['x-status']
+        elif isinstance(message, BabylMessage):
+            flags = set(self.get_flags())
+            if 'R' not in flags:
+                message.add_label('unseen')
+            if 'D' in flags:
+                message.add_label('deleted')
+            if 'A' in flags:
+                message.add_label('answered')
+            del message['status']
+            del message['x-status']
+        elif isinstance(message, Message):
+            pass
+        else:
+            raise TypeError('Cannot convert to specified type: %s' %
+                            type(message))
+
+
+class mboxMessage(_mboxMMDFMessage):
+    """Message with mbox-specific properties."""
+
+
+class MHMessage(Message):
+    """Message with MH-specific properties."""
+
+    def __init__(self, message=None):
+        """Initialize an MHMessage instance."""
+        self._sequences = []
+        Message.__init__(self, message)
+
+    def get_sequences(self):
+        """Return a list of sequences that include the message."""
+        return self._sequences[:]
+
+    def set_sequences(self, sequences):
+        """Set the list of sequences that include the message."""
+        self._sequences = list(sequences)
+
+    def add_sequence(self, sequence):
+        """Add sequence to list of sequences including the message."""
+        if isinstance(sequence, str):
+            if not sequence in self._sequences:
+                self._sequences.append(sequence)
+        else:
+            raise TypeError('sequence must be a string: %s' % type(sequence))
+
+    def remove_sequence(self, sequence):
+        """Remove sequence from the list of sequences including the message."""
+        try:
+            self._sequences.remove(sequence)
+        except ValueError:
+            pass
+
+    def _explain_to(self, message):
+        """Copy MH-specific state to message insofar as possible."""
+        if isinstance(message, MaildirMessage):
+            sequences = set(self.get_sequences())
+            if 'unseen' in sequences:
+                message.set_subdir('cur')
+            else:
+                message.set_subdir('cur')
+                message.add_flag('S')
+            if 'flagged' in sequences:
+                message.add_flag('F')
+            if 'replied' in sequences:
+                message.add_flag('R')
+        elif isinstance(message, _mboxMMDFMessage):
+            sequences = set(self.get_sequences())
+            if 'unseen' not in sequences:
+                message.add_flag('RO')
+            else:
+                message.add_flag('O')
+            if 'flagged' in sequences:
+                message.add_flag('F')
+            if 'replied' in sequences:
+                message.add_flag('A')
+        elif isinstance(message, MHMessage):
+            for sequence in self.get_sequences():
+                message.add_sequence(sequence)
+        elif isinstance(message, BabylMessage):
+            sequences = set(self.get_sequences())
+            if 'unseen' in sequences:
+                message.add_label('unseen')
+            if 'replied' in sequences:
+                message.add_label('answered')
+        elif isinstance(message, Message):
+            pass
+        else:
+            raise TypeError('Cannot convert to specified type: %s' %
+                            type(message))
+
+
+class BabylMessage(Message):
+    """Message with Babyl-specific properties."""
+
+    def __init__(self, message=None):
+        """Initialize an BabylMessage instance."""
+        self._labels = []
+        self._visible = Message()
+        Message.__init__(self, message)
+
+    def get_labels(self):
+        """Return a list of labels on the message."""
+        return self._labels[:]
+
+    def set_labels(self, labels):
+        """Set the list of labels on the message."""
+        self._labels = list(labels)
+
+    def add_label(self, label):
+        """Add label to list of labels on the message."""
+        if isinstance(label, str):
+            if label not in self._labels:
+                self._labels.append(label)
+        else:
+            raise TypeError('label must be a string: %s' % type(label))
+
+    def remove_label(self, label):
+        """Remove label from the list of labels on the message."""
+        try:
+            self._labels.remove(label)
+        except ValueError:
+            pass
+    
+    def get_visible(self):
+        """Return a Message representation of visible headers."""
+        return Message(self._visible)
+
+    def set_visible(self, visible):
+        """Set the Message representation of visible headers."""
+        self._visible = Message(visible)
+
+    def update_visible(self):
+        """Update and/or sensibly generate a set of visible headers."""
+        for header in self._visible.keys():
+            if header in self:
+                self._visible.replace_header(header, self[header])
+            else:
+                del self._visible[header]
+        for header in ('Date', 'From', 'Reply-To', 'To', 'CC', 'Subject'):
+            if header in self and header not in self._visible:
+                self._visible[header] = self[header]
+
+    def _explain_to(self, message):
+        """Copy Babyl-specific state to message insofar as possible."""
+        if isinstance(message, MaildirMessage):
+            labels = set(self.get_labels())
+            if 'unseen' in labels:
+                message.set_subdir('cur')
+            else:
+                message.set_subdir('cur')
+                message.add_flag('S')
+            if 'forwarded' in labels or 'resent' in labels:
+                message.add_flag('P')
+            if 'answered' in labels:
+                message.add_flag('R')
+            if 'deleted' in labels:
+                message.add_flag('T')
+        elif isinstance(message, _mboxMMDFMessage):
+            labels = set(self.get_labels())
+            if 'unseen' not in labels:
+                message.add_flag('RO')
+            else:
+                message.add_flag('O')
+            if 'deleted' in labels:
+                message.add_flag('D')
+            if 'answered' in labels:
+                message.add_flag('A')
+        elif isinstance(message, MHMessage):
+            labels = set(self.get_labels())
+            if 'unseen' in labels:
+                message.add_sequence('unseen')
+            if 'answered' in labels:
+                message.add_sequence('replied')
+        elif isinstance(message, BabylMessage):
+            message.set_visible(self.get_visible())
+            for label in self.get_labels():
+                message.add_label(label)
+        elif isinstance(message, Message):
+            pass
+        else:
+            raise TypeError('Cannot convert to specified type: %s' %
+                            type(message))
+
+
+class MMDFMessage(_mboxMMDFMessage):
+    """Message with MMDF-specific properties."""
+
+
+class _ProxyFile:
+    """A read-only wrapper of a file."""
+
+    def __init__(self, f, pos=None):
+        """Initialize a _ProxyFile."""
+        self._file = f
+        if pos is None:
+            self._pos = f.tell()
+        else:
+            self._pos = pos
+
+    def read(self, size=None):
+        """Read bytes."""
+        return self._read(size, self._file.read)
+
+    def readline(self, size=None):
+        """Read a line."""
+        return self._read(size, self._file.readline)
+
+    def readlines(self, sizehint=None):
+        """Read multiple lines."""
+        result = []
+        for line in self:
+            result.append(line)
+            if sizehint is not None:
+                sizehint -= len(line)
                 if sizehint <= 0:
                     break
-        return lines
+        return result
+
+    def __iter__(self):
+        """Iterate over lines."""
+        return iter(self.readline, "")
 
     def tell(self):
-        return self.pos - self.start
+        """Return the position."""
+        return self._pos
 
-    def seek(self, pos, whence=0):
+    def seek(self, offset, whence=0):
+        """Change position."""
+        if whence == 1:
+            self._file.seek(self._pos)
+        self._file.seek(offset, whence)
+        self._pos = self._file.tell()
+
+    def close(self):
+        """Close the file."""
+        del self._file
+
+    def _read(self, size, read_method):
+        """Read size bytes using read_method."""
+        if size is None:
+            size = -1
+        self._file.seek(self._pos)
+        result = read_method(size)
+        self._pos = self._file.tell()
+        return result
+
+
+class _PartialFile(_ProxyFile):
+    """A read-only wrapper of part of a file."""
+
+    def __init__(self, f, start=None, stop=None):
+        """Initialize a _PartialFile."""
+        _ProxyFile.__init__(self, f, start)
+        self._start = start
+        self._stop = stop
+
+    def tell(self):
+        """Return the position with respect to start."""
+        return _ProxyFile.tell(self) - self._start
+
+    def seek(self, offset, whence=0):
+        """Change position, possibly with respect to start or stop."""
         if whence == 0:
-            self.pos = self.start + pos
-        elif whence == 1:
-            self.pos = self.pos + pos
+            self._pos = self._start
+            whence = 1
         elif whence == 2:
-            self.pos = self.stop + pos
+            self._pos = self._stop
+            whence = 1
+        _ProxyFile.seek(self, offset, whence)
 
-    def close(self):
-        del self.fp
+    def _read(self, size, read_method):
+        """Read size bytes using read_method, honoring start and stop."""
+        remaining = self._stop - self._pos
+        if remaining <= 0:
+            return ''
+        if size is None or size < 0 or size > remaining:
+            size = remaining
+        return _ProxyFile._read(self, size, read_method)
+
+
+def _lock_file(f, dotlock=True):
+    """Lock file f using lockf, flock, and dot locking."""
+    dotlock_done = False
+    try:
+        if fcntl:
+            try:
+                fcntl.lockf(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            except IOError, e:
+                if e.errno == errno.EAGAIN:
+                    raise ExternalClashError('lockf: lock unavailable: %s' %
+                                             f.name)
+                else:
+                    raise
+            try:
+                fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            except IOError, e:
+                if e.errno == errno.EWOULDBLOCK:
+                    raise ExternalClashError('flock: lock unavailable: %s' %
+                                             f.name)
+                else:
+                    raise
+        if dotlock:
+            try:
+                pre_lock = _create_temporary(f.name + '.lock')
+                pre_lock.close()
+            except IOError, e:
+                if e.errno == errno.EACCES:
+                    return  # Without write access, just skip dotlocking.
+                else:
+                    raise
+            try:
+                if hasattr(os, 'link'):
+                    os.link(pre_lock.name, f.name + '.lock')
+                    dotlock_done = True
+                    os.unlink(pre_lock.name)
+                else:
+                    os.rename(pre_lock.name, f.name + '.lock')
+                    dotlock_done = True
+            except OSError, e:
+                if e.errno == errno.EEXIST:
+                    os.remove(pre_lock.name)
+                    raise ExternalClashError('dot lock unavailable: %s' % 
+                                             f.name)
+                else:
+                    raise
+    except:
+        if fcntl:
+            fcntl.lockf(f, fcntl.LOCK_UN)
+            fcntl.flock(f, fcntl.LOCK_UN)
+        if dotlock_done:
+            os.remove(f.name + '.lock')
+        raise
+
+def _unlock_file(f):
+    """Unlock file f using lockf, flock, and dot locking."""
+    if fcntl:
+        fcntl.lockf(f, fcntl.LOCK_UN)
+        fcntl.flock(f, fcntl.LOCK_UN)
+    if os.path.exists(f.name + '.lock'):
+        os.remove(f.name + '.lock')
+
+def _create_carefully(path):
+    """Create a file if it doesn't exist and open for reading and writing."""
+    fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_RDWR)
+    try:
+        return file(path, 'rb+')
+    finally:
+        os.close(fd)
+
+def _create_temporary(path):
+    """Create a temp file based on path and open for reading and writing."""
+    return _create_carefully('%s.%s.%s.%s' % (path, int(time.time()),
+                                              socket.gethostname(),
+                                              os.getpid()))
 
 
+## Start: classes from the original module (for backward compatibility).
+
+# Note that the Maildir class, whose name is unchanged, itself offers a next()
+# method for backward compatibility.
+
+class _Mailbox:
+
+    def __init__(self, fp, factory=rfc822.Message):
+        self.fp = fp
+        self.seekp = 0
+        self.factory = factory
+
+    def __iter__(self):
+        return iter(self.next, None)
+
+    def next(self):
+        while 1:
+            self.fp.seek(self.seekp)
+            try:
+                self._search_start()
+            except EOFError:
+                self.seekp = self.fp.tell()
+                return None
+            start = self.fp.tell()
+            self._search_end()
+            self.seekp = stop = self.fp.tell()
+            if start != stop:
+                break
+        return self.factory(_PartialFile(self.fp, start, stop))
+
 # Recommended to use PortableUnixMailbox instead!
 class UnixMailbox(_Mailbox):
 
@@ -213,36 +2029,6 @@ class MHMailbox:
         return msg
 
 
-class Maildir:
-    # Qmail directory mailbox
-
-    def __init__(self, dirname, factory=rfc822.Message):
-        self.dirname = dirname
-        self.factory = factory
-
-        # check for new mail
-        newdir = os.path.join(self.dirname, 'new')
-        boxes = [os.path.join(newdir, f)
-                 for f in os.listdir(newdir) if f[0] != '.']
-
-        # Now check for current mail in this maildir
-        curdir = os.path.join(self.dirname, 'cur')
-        boxes += [os.path.join(curdir, f)
-                  for f in os.listdir(curdir) if f[0] != '.']
-        boxes.reverse()
-        self.boxes = boxes
-
-    def __iter__(self):
-        return iter(self.next, None)
-
-    def next(self):
-        if not self.boxes:
-            return None
-        fn = self.boxes.pop()
-        fp = open(fn)
-        return self.factory(fp)
-
-
 class BabylMailbox(_Mailbox):
 
     def _search_start(self):
@@ -263,59 +2049,20 @@ class BabylMailbox(_Mailbox):
                 self.fp.seek(pos)
                 return
 
+## End: classes from the original module (for backward compatibility).
 
-def _test():
-    import sys
 
-    args = sys.argv[1:]
-    if not args:
-        for key in 'MAILDIR', 'MAIL', 'LOGNAME', 'USER':
-            if key in os.environ:
-                mbox = os.environ[key]
-                break
-        else:
-            print "$MAIL, $LOGNAME nor $USER set -- who are you?"
-            return
-    else:
-        mbox = args[0]
-    if mbox[:1] == '+':
-        mbox = os.environ['HOME'] + '/Mail/' + mbox[1:]
-    elif not '/' in mbox:
-        if os.path.isfile('/var/mail/' + mbox):
-            mbox = '/var/mail/' + mbox
-        else:
-            mbox = '/usr/mail/' + mbox
-    if os.path.isdir(mbox):
-        if os.path.isdir(os.path.join(mbox, 'cur')):
-            mb = Maildir(mbox)
-        else:
-            mb = MHMailbox(mbox)
-    else:
-        fp = open(mbox, 'r')
-        mb = PortableUnixMailbox(fp)
+class Error(Exception):
+    """Raised for module-specific errors."""
 
-    msgs = []
-    while 1:
-        msg = mb.next()
-        if msg is None:
-            break
-        msgs.append(msg)
-        if len(args) <= 1:
-            msg.fp = None
-    if len(args) > 1:
-        num = int(args[1])
-        print 'Message %d body:'%num
-        msg = msgs[num-1]
-        msg.rewindbody()
-        sys.stdout.write(msg.fp.read())
-    else:
-        print 'Mailbox',mbox,'has',len(msgs),'messages:'
-        for msg in msgs:
-            f = msg.getheader('from') or ""
-            s = msg.getheader('subject') or ""
-            d = msg.getheader('date') or ""
-            print '-%20.20s   %20.20s   %-30.30s'%(f, d[5:], s)
-
-
-if __name__ == '__main__':
-    _test()
+class NoSuchMailboxError(Error):
+    """The specified mailbox does not exist and won't be created."""
+
+class NotEmptyError(Error):
+    """The specified mailbox is not empty and deletion was requested."""
+
+class ExternalClashError(Error):
+    """Another process caused an action to fail."""
+
+class FormatError(Error):
+    """A file appears to have an invalid format."""

Lib/test/test_mailbox.py

-import mailbox
 import os
 import time
-import unittest
+import stat
+import socket
+import email
+import email.Message
+import rfc822
+import re
+import StringIO
 from test import test_support
-
-# cleanup earlier tests
+import unittest
+import mailbox
+import glob
 try:
-    os.unlink(test_support.TESTFN)
-except os.error:
+    import fcntl
+except ImportError:
     pass
 
+
+class TestBase(unittest.TestCase):
+
+    def _check_sample(self, msg):
+        # Inspect a mailbox.Message representation of the sample message
+        self.assert_(isinstance(msg, email.Message.Message))
+        self.assert_(isinstance(msg, mailbox.Message))
+        for key, value in _sample_headers.iteritems():
+            self.assert_(value in msg.get_all(key))
+        self.assert_(msg.is_multipart())
+        self.assert_(len(msg.get_payload()) == len(_sample_payloads))
+        for i, payload in enumerate(_sample_payloads):
+            part = msg.get_payload(i)
+            self.assert_(isinstance(part, email.Message.Message))
+            self.assert_(not isinstance(part, mailbox.Message))
+            self.assert_(part.get_payload() == payload)
+
+    def _delete_recursively(self, target):
+        # Delete a file or delete a directory recursively
+        if os.path.isdir(target):
+            for path, dirs, files in os.walk(target, topdown=False):
+                for name in files:
+                    os.remove(os.path.join(path, name))
+                for name in dirs:
+                    os.rmdir(os.path.join(path, name))
+            os.rmdir(target)
+        elif os.path.exists(target):
+            os.remove(target)
+
+
+class TestMailbox(TestBase):
+
+    _factory = None     # Overridden by subclasses to reuse tests
+    _template = 'From: foo\n\n%s'
+
+    def setUp(self):
+        self._path = test_support.TESTFN
+        self._box = self._factory(self._path)
+
+    def tearDown(self):
+        self._box.close()
+        self._delete_recursively(self._path)
+
+    def test_add(self):
+        # Add copies of a sample message
+        keys = []
+        keys.append(self._box.add(self._template % 0))
+        self.assert_(len(self._box) == 1)
+        keys.append(self._box.add(mailbox.Message(_sample_message)))
+        self.assert_(len(self._box) == 2)
+        keys.append(self._box.add(email.message_from_string(_sample_message)))
+        self.assert_(len(self._box) == 3)
+        keys.append(self._box.add(StringIO.StringIO(_sample_message)))
+        self.assert_(len(self._box) == 4)
+        keys.append(self._box.add(_sample_message))
+        self.assert_(len(self._box) == 5)
+        self.assert_(self._box.get_string(keys[0]) == self._template % 0)
+        for i in (1, 2, 3, 4):
+            self._check_sample(self._box[keys[i]])
+
+    def test_remove(self):
+        # Remove messages using remove()
+        self._test_remove_or_delitem(self._box.remove)
+
+    def test_delitem(self):
+        # Remove messages using __delitem__()
+        self._test_remove_or_delitem(self._box.__delitem__)
+
+    def _test_remove_or_delitem(self, method):
+        # (Used by test_remove() and test_delitem().)
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(self._template % 1)
+        self.assert_(len(self._box) == 2)
+        method(key0)
+        l = len(self._box)
+        self.assert_(l == 1, "actual l: %s" % l)
+        self.assertRaises(KeyError, lambda: self._box[key0])
+        self.assertRaises(KeyError, lambda: method(key0))
+        self.assert_(self._box.get_string(key1) == self._template % 1)
+        key2 = self._box.add(self._template % 2)
+        self.assert_(len(self._box) == 2)
+        method(key2)
+        l = len(self._box)
+        self.assert_(l == 1, "actual l: %s" % l)
+        self.assertRaises(KeyError, lambda: self._box[key2])
+        self.assertRaises(KeyError, lambda: method(key2))
+        self.assert_(self._box.get_string(key1) == self._template % 1)
+        method(key1)
+        self.assert_(len(self._box) == 0)
+        self.assertRaises(KeyError, lambda: self._box[key1])
+        self.assertRaises(KeyError, lambda: method(key1))
+
+    def test_discard(self, repetitions=10):
+        # Discard messages
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(self._template % 1)
+        self.assert_(len(self._box) == 2)
+        self._box.discard(key0)
+        self.assert_(len(self._box) == 1)
+        self.assertRaises(KeyError, lambda: self._box[key0])
+        self._box.discard(key0)
+        self.assert_(len(self._box) == 1)
+        self.assertRaises(KeyError, lambda: self._box[key0])
+
+    def test_get(self):
+        # Retrieve messages using get()
+        key0 = self._box.add(self._template % 0)
+        msg = self._box.get(key0)
+        self.assert_(msg['from'] == 'foo')
+        self.assert_(msg.get_payload() == '0')
+        self.assert_(self._box.get('foo') is None)
+        self.assert_(self._box.get('foo', False) is False)
+        self._box.close()
+        self._box = self._factory(self._path, factory=rfc822.Message)
+        key1 = self._box.add(self._template % 1)
+        msg = self._box.get(key1)
+        self.assert_(msg['from'] == 'foo')
+        self.assert_(msg.fp.read() == '1')
+
+    def test_getitem(self):
+        # Retrieve message using __getitem__()
+        key0 = self._box.add(self._template % 0)
+        msg = self._box[key0]
+        self.assert_(msg['from'] == 'foo')
+        self.assert_(msg.get_payload() == '0')
+        self.assertRaises(KeyError, lambda: self._box['foo'])
+        self._box.discard(key0)
+        self.assertRaises(KeyError, lambda: self._box[key0])
+
+    def test_get_message(self):
+        # Get Message representations of messages
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(_sample_message)
+        msg0 = self._box.get_message(key0)
+        self.assert_(isinstance(msg0, mailbox.Message))
+        self.assert_(msg0['from'] == 'foo')
+        self.assert_(msg0.get_payload() == '0')
+        self._check_sample(self._box.get_message(key1))
+
+    def test_get_string(self):
+        # Get string representations of messages
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(_sample_message)
+        self.assert_(self._box.get_string(key0) == self._template % 0)
+        self.assert_(self._box.get_string(key1) == _sample_message)
+
+    def test_get_file(self):
+        # Get file representations of messages
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(_sample_message)
+        self.assert_(self._box.get_file(key0).read().replace(os.linesep, '\n')
+                     == self._template % 0)
+        self.assert_(self._box.get_file(key1).read().replace(os.linesep, '\n')
+                     == _sample_message)
+
+    def test_iterkeys(self):
+        # Get keys using iterkeys()
+        self._check_iteration(self._box.iterkeys, do_keys=True, do_values=False)
+
+    def test_keys(self):
+        # Get keys using keys()
+        self._check_iteration(self._box.keys, do_keys=True, do_values=False)
+
+    def test_itervalues(self):
+        # Get values using itervalues()
+        self._check_iteration(self._box.itervalues, do_keys=False,
+                              do_values=True)
+
+    def test_iter(self):
+        # Get values using __iter__()
+        self._check_iteration(self._box.__iter__, do_keys=False,
+                              do_values=True)
+
+    def test_values(self):
+        # Get values using values()
+        self._check_iteration(self._box.values, do_keys=False, do_values=True)
+
+    def test_iteritems(self):
+        # Get keys and values using iteritems()
+        self._check_iteration(self._box.iteritems, do_keys=True,
+                              do_values=True)
+
+    def test_items(self):
+        # Get keys and values using items()
+        self._check_iteration(self._box.items, do_keys=True, do_values=True)
+
+    def _check_iteration(self, method, do_keys, do_values, repetitions=10):
+        for value in method():
+            self.fail("Not empty")
+        keys, values = [], []
+        for i in xrange(repetitions):
+            keys.append(self._box.add(self._template % i))
+            values.append(self._template % i)
+        if do_keys and not do_values:
+            returned_keys = list(method())
+        elif do_values and not do_keys:
+            returned_values = list(method())
+        else:
+            returned_keys, returned_values = [], []
+            for key, value in method():
+                returned_keys.append(key)
+                returned_values.append(value)
+        if do_keys:
+            self.assert_(len(keys) == len(returned_keys))
+            self.assert_(set(keys) == set(returned_keys))
+        if do_values:
+            count = 0
+            for value in returned_values:
+                self.assert_(value['from'] == 'foo')
+                self.assert_(int(value.get_payload()) < repetitions)
+                count += 1
+            self.assert_(len(values) == count)
+
+    def test_has_key(self):
+        # Check existence of keys using has_key()
+        self._test_has_key_or_contains(self._box.has_key)
+
+    def test_contains(self):
+        # Check existence of keys using __contains__()
+        self._test_has_key_or_contains(self._box.__contains__)
+
+    def _test_has_key_or_contains(self, method):
+        # (Used by test_has_key() and test_contains().)
+        self.assert_(not method('foo'))
+        key0 = self._box.add(self._template % 0)
+        self.assert_(method(key0))
+        self.assert_(not method('foo'))
+        key1 = self._box.add(self._template % 1)
+        self.assert_(method(key1))
+        self.assert_(method(key0))
+        self.assert_(not method('foo'))
+        self._box.remove(key0)
+        self.assert_(not method(key0))
+        self.assert_(method(key1))
+        self.assert_(not method('foo'))
+        self._box.remove(key1)
+        self.assert_(not method(key1))
+        self.assert_(not method(key0))
+        self.assert_(not method('foo'))
+
+    def test_len(self, repetitions=10):
+        # Get message count
+        keys = []
+        for i in xrange(repetitions):
+            self.assert_(len(self._box) == i)
+            keys.append(self._box.add(self._template % i))
+            self.assert_(len(self._box) == i + 1)
+        for i in xrange(repetitions):
+            self.assert_(len(self._box) == repetitions - i)
+            self._box.remove(keys[i])
+            self.assert_(len(self._box) == repetitions - i - 1)
+
+    def test_set_item(self):
+        # Modify messages using __setitem__()
+        key0 = self._box.add(self._template % 'original 0')
+        self.assert_(self._box.get_string(key0) == \
+                     self._template % 'original 0')
+        key1 = self._box.add(self._template % 'original 1')
+        self.assert_(self._box.get_string(key1) == \
+                     self._template % 'original 1')
+        self._box[key0] = self._template % 'changed 0'
+        self.assert_(self._box.get_string(key0) == \
+                     self._template % 'changed 0')
+        self._box[key1] = self._template % 'changed 1'
+        self.assert_(self._box.get_string(key1) == \
+                     self._template % 'changed 1')
+        self._box[key0] = _sample_message
+        self._check_sample(self._box[key0])
+        self._box[key1] = self._box[key0]
+        self._check_sample(self._box[key1])
+        self._box[key0] = self._template % 'original 0'
+        self.assert_(self._box.get_string(key0) ==
+                     self._template % 'original 0')
+        self._check_sample(self._box[key1])
+        self.assertRaises(KeyError,
+                          lambda: self._box.__setitem__('foo', 'bar'))
+        self.assertRaises(KeyError, lambda: self._box['foo'])
+        self.assert_(len(self._box) == 2)
+
+    def test_clear(self, iterations=10):
+        # Remove all messages using clear()
+        keys = []
+        for i in xrange(iterations):
+            self._box.add(self._template % i)
+        for i, key in enumerate(keys):
+            self.assert_(self._box.get_string(key) == self._template % i)
+        self._box.clear()
+        self.assert_(len(self._box) == 0)
+        for i, key in enumerate(keys):
+            self.assertRaises(KeyError, lambda: self._box.get_string(key))
+
+    def test_pop(self):
+        # Get and remove a message using pop()
+        key0 = self._box.add(self._template % 0)
+        self.assert_(key0 in self._box)
+        key1 = self._box.add(self._template % 1)
+        self.assert_(key1 in self._box)
+        self.assert_(self._box.pop(key0).get_payload() == '0')
+        self.assert_(key0 not in self._box)
+        self.assert_(key1 in self._box)
+        key2 = self._box.add(self._template % 2)
+        self.assert_(key2 in self._box)
+        self.assert_(self._box.pop(key2).get_payload() == '2')
+        self.assert_(key2 not in self._box)
+        self.assert_(key1 in self._box)
+        self.assert_(self._box.pop(key1).get_payload() == '1')
+        self.assert_(key1 not in self._box)
+        self.assert_(len(self._box) == 0)
+
+    def test_popitem(self, iterations=10):
+        # Get and remove an arbitrary (key, message) using popitem()
+        keys = []
+        for i in xrange(10):
+            keys.append(self._box.add(self._template % i))
+        seen = []
+        for i in xrange(10):
+            key, msg = self._box.popitem()
+            self.assert_(key in keys)
+            self.assert_(key not in seen)
+            seen.append(key)
+            self.assert_(int(msg.get_payload()) == keys.index(key))
+        self.assert_(len(self._box) == 0)
+        for key in keys:
+            self.assertRaises(KeyError, lambda: self._box[key])
+
+    def test_update(self):
+        # Modify multiple messages using update()
+        key0 = self._box.add(self._template % 'original 0')
+        key1 = self._box.add(self._template % 'original 1')
+        key2 = self._box.add(self._template % 'original 2')
+        self._box.update({key0: self._template % 'changed 0',
+                          key2: _sample_message})
+        self.assert_(len(self._box) == 3)
+        self.assert_(self._box.get_string(key0) ==
+                     self._template % 'changed 0')
+        self.assert_(self._box.get_string(key1) ==
+                     self._template % 'original 1')
+        self._check_sample(self._box[key2])
+        self._box.update([(key2, self._template % 'changed 2'),
+                    (key1, self._template % 'changed 1'),
+                    (key0, self._template % 'original 0')])
+        self.assert_(len(self._box) == 3)
+        self.assert_(self._box.get_string(key0) ==
+                     self._template % 'original 0')
+        self.assert_(self._box.get_string(key1) ==
+                     self._template % 'changed 1')
+        self.assert_(self._box.get_string(key2) ==
+                     self._template % 'changed 2')
+        self.assertRaises(KeyError,
+                          lambda: self._box.update({'foo': 'bar',
+                                          key0: self._template % "changed 0"}))
+        self.assert_(len(self._box) == 3)
+        self.assert_(self._box.get_string(key0) ==
+                     self._template % "changed 0")
+        self.assert_(self._box.get_string(key1) ==
+                     self._template % "changed 1")
+        self.assert_(self._box.get_string(key2) ==
+                     self._template % "changed 2")
+
+    def test_flush(self):
+        # Write changes to disk
+        self._test_flush_or_close(self._box.flush)
+
+    def test_lock_unlock(self):
+        # Lock and unlock the mailbox
+        self.assert_(not os.path.exists(self._get_lock_path()))
+        self._box.lock()
+        self.assert_(os.path.exists(self._get_lock_path()))
+        self._box.unlock()
+        self.assert_(not os.path.exists(self._get_lock_path()))
+
+    def test_close(self):
+        # Close mailbox and flush changes to disk
+        self._test_flush_or_close(self._box.close)
+
+    def _test_flush_or_close(self, method):
+        contents = [self._template % i for i in xrange(3)]
+        self._box.add(contents[0])
+        self._box.add(contents[1])
+        self._box.add(contents[2])
+        method()
+        self._box = self._factory(self._path)
+        keys = self._box.keys()
+        self.assert_(len(keys) == 3)
+        for key in keys:
+            self.assert_(self._box.get_string(key) in contents)
+
+    def test_dump_message(self):
+        # Write message representations to disk
+        for input in (email.message_from_string(_sample_message),
+                      _sample_message, StringIO.StringIO(_sample_message)):
+            output = StringIO.StringIO()
+            self._box._dump_message(input, output)
+            self.assert_(output.getvalue() ==
+                         _sample_message.replace('\n', os.linesep))
+        output = StringIO.StringIO()
+        self.assertRaises(TypeError,
+                          lambda: self._box._dump_message(None, output))
+
+    def _get_lock_path(self):
+        # Return the path of the dot lock file. May be overridden.
+        return self._path + '.lock'
+
+
+class TestMailboxSuperclass(TestBase):
+
+    def test_notimplemented(self):
+        # Test that all Mailbox methods raise NotImplementedException.
+        box = mailbox.Mailbox('path')
+        self.assertRaises(NotImplementedError, lambda: box.add(''))
+        self.assertRaises(NotImplementedError, lambda: box.remove(''))
+        self.assertRaises(NotImplementedError, lambda: box.__delitem__(''))
+        self.assertRaises(NotImplementedError, lambda: box.discard(''))
+        self.assertRaises(NotImplementedError, lambda: box.__setitem__('', ''))
+        self.assertRaises(NotImplementedError, lambda: box.iterkeys())
+        self.assertRaises(NotImplementedError, lambda: box.keys())
+        self.assertRaises(NotImplementedError, lambda: box.itervalues().next())
+        self.assertRaises(NotImplementedError, lambda: box.__iter__().next())
+        self.assertRaises(NotImplementedError, lambda: box.values())
+        self.assertRaises(NotImplementedError, lambda: box.iteritems().next())
+        self.assertRaises(NotImplementedError, lambda: box.items())
+        self.assertRaises(NotImplementedError, lambda: box.get(''))
+        self.assertRaises(NotImplementedError, lambda: box.__getitem__(''))
+        self.assertRaises(NotImplementedError, lambda: box.get_message(''))
+        self.assertRaises(NotImplementedError, lambda: box.get_string(''))
+        self.assertRaises(NotImplementedError, lambda: box.get_file(''))
+        self.assertRaises(NotImplementedError, lambda: box.has_key(''))
+        self.assertRaises(NotImplementedError, lambda: box.__contains__(''))
+        self.assertRaises(NotImplementedError, lambda: box.__len__())
+        self.assertRaises(NotImplementedError, lambda: box.clear())
+        self.assertRaises(NotImplementedError, lambda: box.pop(''))
+        self.assertRaises(NotImplementedError, lambda: box.popitem())
+        self.assertRaises(NotImplementedError, lambda: box.update((('', ''),)))
+        self.assertRaises(NotImplementedError, lambda: box.flush())
+        self.assertRaises(NotImplementedError, lambda: box.lock())
+        self.assertRaises(NotImplementedError, lambda: box.unlock())
+        self.assertRaises(NotImplementedError, lambda: box.close())
+
+
+class TestMaildir(TestMailbox):
+
+    _factory = lambda self, path, factory=None: mailbox.Maildir(path, factory)
+
+    def setUp(self):
+        TestMailbox.setUp(self)
+        if os.name == 'nt':
+            self._box.colon = '!'
+
+    def test_add_MM(self):
+        # Add a MaildirMessage instance
+        msg = mailbox.MaildirMessage(self._template % 0)
+        msg.set_subdir('cur')
+        msg.set_info('foo')
+        key = self._box.add(msg)
+        self.assert_(os.path.exists(os.path.join(self._path, 'cur', '%s%sfoo' %
+                                                 (key, self._box.colon))))
+
+    def test_get_MM(self):
+        # Get a MaildirMessage instance
+        msg = mailbox.MaildirMessage(self._template % 0)
+        msg.set_subdir('cur')
+        msg.set_flags('RF')
+        key = self._box.add(msg)
+        msg_returned = self._box.get_message(key)
+        self.assert_(isinstance(msg_returned, mailbox.MaildirMessage))
+        self.assert_(msg_returned.get_subdir() == 'cur')
+        self.assert_(msg_returned.get_flags() == 'FR')
+
+    def test_set_MM(self):
+        # Set with a MaildirMessage instance
+        msg0 = mailbox.MaildirMessage(self._template % 0)
+        msg0.set_flags('TP')
+        key = self._box.add(msg0)
+        msg_returned = self._box.get_message(key)
+        self.assert_(msg_returned.get_subdir() == 'new')
+        self.assert_(msg_returned.get_flags() == 'PT')
+        msg1 = mailbox.MaildirMessage(self._template % 1)
+        self._box[key] = msg1
+        msg_returned = self._box.get_message(key)
+        self.assert_(msg_returned.get_subdir() == 'new')
+        self.assert_(msg_returned.get_flags() == '')
+        self.assert_(msg_returned.get_payload() == '1')
+        msg2 = mailbox.MaildirMessage(self._template % 2)
+        msg2.set_info('2,S')
+        self._box[key] = msg2
+        self._box[key] = self._template % 3
+        msg_returned = self._box.get_message(key)
+        self.assert_(msg_returned.get_subdir() == 'new')
+        self.assert_(msg_returned.get_flags() == 'S')
+        self.assert_(msg_returned.get_payload() == '3')
+
+    def test_initialize_new(self):
+        # Initialize a non-existent mailbox
+        self.tearDown()
+        self._box = mailbox.Maildir(self._path)
+        self._check_basics(factory=rfc822.Message)
+        self._delete_recursively(self._path)
+        self._box = self._factory(self._path, factory=None)
+        self._check_basics()
+
+    def test_initialize_existing(self):
+        # Initialize an existing mailbox
+        self.tearDown()
+        for subdir in '', 'tmp', 'new', 'cur':
+            os.mkdir(os.path.join(self._path, subdir))
+        self._box = mailbox.Maildir(self._path)
+        self._check_basics(factory=rfc822.Message)
+        self._box = mailbox.Maildir(self._path, factory=None)
+        self._check_basics()
+
+    def _check_basics(self, factory=None):
+        # (Used by test_open_new() and test_open_existing().)
+        self.assertEqual(self._box._path, os.path.abspath(self._path))
+        self.assertEqual(self._box._factory, factory)
+        for subdir in '', 'tmp', 'new', 'cur':
+            path = os.path.join(self._path, subdir)
+            mode = os.stat(path)[stat.ST_MODE]
+            self.assert_(stat.S_ISDIR(mode), "Not a directory: '%s'" % path)
+
+    def test_list_folders(self):
+        # List folders
+        self._box.add_folder('one')
+        self._box.add_folder('two')
+        self._box.add_folder('three')
+        self.assert_(len(self._box.list_folders()) == 3)
+        self.assert_(set(self._box.list_folders()) ==
+                     set(('one', 'two', 'three')))
+
+    def test_get_folder(self):
+        # Open folders
+        self._box.add_folder('foo.bar')
+        folder0 = self._box.get_folder('foo.bar')
+        folder0.add(self._template % 'bar')
+        self.assert_(os.path.isdir(os.path.join(self._path, '.foo.bar')))
+        folder1 = self._box.get_folder('foo.bar')
+        self.assert_(folder1.get_string(folder1.keys()[0]) == \
+                     self._template % 'bar')
+
+    def test_add_and_remove_folders(self):
+        # Delete folders
+        self._box.add_folder('one')
+        self._box.add_folder('two')
+        self.assert_(len(self._box.list_folders()) == 2)
+        self.assert_(set(self._box.list_folders()) == set(('one', 'two')))
+        self._box.remove_folder('one')
+        self.assert_(len(self._box.list_folders()) == 1)
+        self.assert_(set(self._box.list_folders()) == set(('two',)))
+        self._box.add_folder('three')
+        self.assert_(len(self._box.list_folders()) == 2)
+        self.assert_(set(self._box.list_folders()) == set(('two', 'three')))
+        self._box.remove_folder('three')
+        self.assert_(len(self._box.list_folders()) == 1)
+        self.assert_(set(self._box.list_folders()) == set(('two',)))
+        self._box.remove_folder('two')
+        self.assert_(len(self._box.list_folders()) == 0)
+        self.assert_(self._box.list_folders() == [])
+
+    def test_clean(self):
+        # Remove old files from 'tmp'
+        foo_path = os.path.join(self._path, 'tmp', 'foo')
+        bar_path = os.path.join(self._path, 'tmp', 'bar')
+        file(foo_path, 'w').close()
+        file(bar_path, 'w').close()
+        self._box.clean()
+        self.assert_(os.path.exists(foo_path))
+        self.assert_(os.path.exists(bar_path))
+        foo_stat = os.stat(foo_path)
+        os.utime(os.path.join(foo_path), (time.time() - 129600 - 2,
+                                          foo_stat.st_mtime))
+        self._box.clean()
+        self.assert_(not os.path.exists(foo_path))
+        self.assert_(os.path.exists(bar_path))
+
+    def test_create_tmp(self, repetitions=10):
+        # Create files in tmp directory
+        hostname = socket.gethostname()
+        if '/' in hostname:
+            hostname = hostname.replace('/', r'\057')
+        if ':' in hostname:
+            hostname = hostname.replace(':', r'\072')
+        pid = os.getpid()
+        pattern = re.compile(r"(?P<time>\d+)\.M(?P<M>\d{1,6})P(?P<P>\d+)"
+                             r"Q(?P<Q>\d+)\.(?P<host>[^:/]+)")
+        previous_groups = None
+        for x in xrange(repetitions):
+            tmp_file = self._box._create_tmp()
+            head, tail = os.path.split(tmp_file.name)
+            self.assertEqual(head, os.path.abspath(os.path.join(self._path,
+                                                                "tmp")),
+                             "File in wrong location: '%s'" % head)
+            match = pattern.match(tail)
+            self.assert_(match != None, "Invalid file name: '%s'" % tail)
+            groups = match.groups()
+            if previous_groups != None:
+                self.assert_(int(groups[0] >= previous_groups[0]),
+                             "Non-monotonic seconds: '%s' before '%s'" %
+                             (previous_groups[0], groups[0]))
+                self.assert_(int(groups[1] >= previous_groups[1]) or
+                             groups[0] != groups[1],
+                             "Non-monotonic milliseconds: '%s' before '%s'" %
+                             (previous_groups[1], groups[1]))
+                self.assert_(int(groups[2]) == pid,
+                             "Process ID mismatch: '%s' should be '%s'" %
+                             (groups[2], pid))
+                self.assert_(int(groups[3]) == int(previous_groups[3]) + 1,
+                             "Non-sequential counter: '%s' before '%s'" %
+                             (previous_groups[3], groups[3]))
+                self.assert_(groups[4] == hostname,
+                             "Host name mismatch: '%s' should be '%s'" %
+                             (groups[4], hostname))
+            previous_groups = groups
+            tmp_file.write(_sample_message)
+            tmp_file.seek(0)
+            self.assert_(tmp_file.read() == _sample_message)
+            tmp_file.close()
+        file_count = len(os.listdir(os.path.join(self._path, "tmp")))
+        self.assert_(file_count == repetitions,
+                     "Wrong file count: '%s' should be '%s'" %
+                     (file_count, repetitions))
+
+    def test_refresh(self):
+        # Update the table of contents
+        self.assert_(self._box._toc == {})
+        key0 = self._box.add(self._template % 0)
+        key1 = self._box.add(self._template % 1)
+        self.assert_(self._box._toc == {})
+        self._box._refresh()
+        self.assert_(self._box._toc == {key0: os.path.join('new', key0),
+                                        key1: os.path.join('new', key1)})
+        key2 = self._box.add(self._template % 2)
+        self.assert_(self._box._toc == {key0: os.path.join('new', key0),
+                                        key1: os.path.join('new', key1)})
+        self._box._refresh()
+        self.assert_(self._box._toc == {key0: os.path.join('new', key0),
+                                        key1: os.path.join('new', key1),
+                                        key2: os.path.join('new', key2)})
+
+    def test_lookup(self):
+        # Look up message subpaths in the TOC
+        self.assertRaises(KeyError, lambda: self._box._lookup('foo'))
+        key0 = self._box.add(self._template % 0)
+        self.assert_(self._box._lookup(key0) == os.path.join('new', key0))
+        os.remove(os.path.join(self._path, 'new', key0))
+        self.assert_(self._box._toc == {key0: os.path.join('new', key0)})
+        self.assertRaises(KeyError, lambda: self._box._lookup(key0))
+        self.assert_(self._box._toc == {})
+
+    def test_lock_unlock(self):
+        # Lock and unlock the mailbox. For Maildir, this does nothing.
+        self._box.lock()
+        self._box.unlock()
+
+
+class _TestMboxMMDF(TestMailbox):
+
+    def tearDown(self):
+        self._box.close()
+        self._delete_recursively(self._path)
+        for lock_remnant in glob.glob(self._path + '.*'):
+            os.remove(lock_remnant)
+
+    def test_add_from_string(self):
+        # Add a string starting with 'From ' to the mailbox
+        key = self._box.add('From foo@bar blah\nFrom: foo\n\n0')
+        self.assert_(self._box[key].get_from() == 'foo@bar blah')
+        self.assert_(self._box[key].get_payload() == '0')
+
+    def test_add_mbox_or_mmdf_message(self):
+        # Add an mboxMessage or MMDFMessage
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg = class_('From foo@bar blah\nFrom: foo\n\n0')
+            key = self._box.add(msg)
+
+    def test_open_close_open(self):
+        # Open and inspect previously-created mailbox
+        values = [self._template % i for i in xrange(3)]
+        for value in values:
+            self._box.add(value)
+        self._box.close()
+        mtime = os.path.getmtime(self._path)
+        self._box = self._factory(self._path)
+        self.assert_(len(self._box) == 3)
+        for key in self._box.iterkeys():
+            self.assert_(self._box.get_string(key) in values)
+        self._box.close()
+        self.assert_(mtime == os.path.getmtime(self._path))
+
+    def test_add_and_close(self):
+        # Verifying that closing a mailbox doesn't change added items
+        self._box.add(_sample_message)
+        for i in xrange(3):
+            self._box.add(self._template % i)
+        self._box.add(_sample_message)
+        self._box._file.flush()
+        self._box._file.seek(0)
+        contents = self._box._file.read()
+        self._box.close()
+        self.assert_(contents == file(self._path, 'rb').read())
+        self._box = self._factory(self._path)
+
+
+class TestMbox(_TestMboxMMDF):
+
+    _factory = lambda self, path, factory=None: mailbox.mbox(path, factory)
+
+
+class TestMMDF(_TestMboxMMDF):
+
+    _factory = lambda self, path, factory=None: mailbox.MMDF(path, factory)
+
+
+class TestMH(TestMailbox):
+
+    _factory = lambda self, path, factory=None: mailbox.MH(path, factory)
+
+    def test_list_folders(self):
+        # List folders
+        self._box.add_folder('one')
+        self._box.add_folder('two')
+        self._box.add_folder('three')
+        self.assert_(len(self._box.list_folders()) == 3)
+        self.assert_(set(self._box.list_folders()) ==
+                     set(('one', 'two', 'three')))
+
+    def test_get_folder(self):
+        # Open folders
+        self._box.add_folder('foo.bar')
+        folder0 = self._box.get_folder('foo.bar')
+        folder0.add(self._template % 'bar')
+        self.assert_(os.path.isdir(os.path.join(self._path, 'foo.bar')))
+        folder1 = self._box.get_folder('foo.bar')
+        self.assert_(folder1.get_string(folder1.keys()[0]) == \
+                     self._template % 'bar')
+
+    def test_add_and_remove_folders(self):
+        # Delete folders
+        self._box.add_folder('one')
+        self._box.add_folder('two')
+        self.assert_(len(self._box.list_folders()) == 2)
+        self.assert_(set(self._box.list_folders()) == set(('one', 'two')))
+        self._box.remove_folder('one')
+        self.assert_(len(self._box.list_folders()) == 1)
+        self.assert_(set(self._box.list_folders()) == set(('two',)))
+        self._box.add_folder('three')
+        self.assert_(len(self._box.list_folders()) == 2)
+        self.assert_(set(self._box.list_folders()) == set(('two', 'three')))
+        self._box.remove_folder('three')
+        self.assert_(len(self._box.list_folders()) == 1)
+        self.assert_(set(self._box.list_folders()) == set(('two',)))
+        self._box.remove_folder('two')
+        self.assert_(len(self._box.list_folders()) == 0)
+        self.assert_(self._box.list_folders() == [])
+
+    def test_sequences(self):
+        # Get and set sequences
+        self.assert_(self._box.get_sequences() == {})
+        msg0 = mailbox.MHMessage(self._template % 0)
+        msg0.add_sequence('foo')
+        key0 = self._box.add(msg0)
+        self.assert_(self._box.get_sequences() == {'foo':[key0]})
+        msg1 = mailbox.MHMessage(self._template % 1)
+        msg1.set_sequences(['bar', 'replied', 'foo'])
+        key1 = self._box.add(msg1)
+        self.assert_(self._box.get_sequences() ==
+                     {'foo':[key0, key1], 'bar':[key1], 'replied':[key1]})
+        msg0.set_sequences(['flagged'])
+        self._box[key0] = msg0
+        self.assert_(self._box.get_sequences() ==
+                     {'foo':[key1], 'bar':[key1], 'replied':[key1],
+                      'flagged':[key0]})
+        self._box.remove(key1)
+        self.assert_(self._box.get_sequences() == {'flagged':[key0]})
+
+    def test_pack(self):
+        # Pack the contents of the mailbox
+        msg0 = mailbox.MHMessage(self._template % 0)
+        msg1 = mailbox.MHMessage(self._template % 1)
+        msg2 = mailbox.MHMessage(self._template % 2)
+        msg3 = mailbox.MHMessage(self._template % 3)
+        msg0.set_sequences(['foo', 'unseen'])
+        msg1.set_sequences(['foo'])
+        msg2.set_sequences(['foo', 'flagged'])
+        msg3.set_sequences(['foo', 'bar', 'replied'])
+        key0 = self._box.add(msg0)
+        key1 = self._box.add(msg1)
+        key2 = self._box.add(msg2)
+        key3 = self._box.add(msg3)
+        self.assert_(self._box.get_sequences() ==
+                     {'foo':[key0,key1,key2,key3], 'unseen':[key0],
+                      'flagged':[key2], 'bar':[key3], 'replied':[key3]})
+        self._box.remove(key2)
+        self.assert_(self._box.get_sequences() ==
+                     {'foo':[key0,key1,key3], 'unseen':[key0], 'bar':[key3],
+                      'replied':[key3]})
+        self._box.pack()
+        self.assert_(self._box.keys() == [1, 2, 3])
+        key0 = key0
+        key1 = key0 + 1
+        key2 = key1 + 1
+        self.assert_(self._box.get_sequences() ==
+                     {'foo':[1, 2, 3], 'unseen':[1], 'bar':[3], 'replied':[3]})
+
+    def _get_lock_path(self):
+        return os.path.join(self._path, '.mh_sequences.lock')
+
+
+class TestBabyl(TestMailbox):
+
+    _factory = lambda self, path, factory=None: mailbox.Babyl(path, factory)
+
+    def tearDown(self):
+        self._box.close()
+        self._delete_recursively(self._path)
+        for lock_remnant in glob.glob(self._path + '.*'):
+            os.remove(lock_remnant)
+
+    def test_labels(self):
+        # Get labels from the mailbox
+        self.assert_(self._box.get_labels() == [])
+        msg0 = mailbox.BabylMessage(self._template % 0)
+        msg0.add_label('foo')
+        key0 = self._box.add(msg0)
+        self.assert_(self._box.get_labels() == ['foo'])
+        msg1 = mailbox.BabylMessage(self._template % 1)
+        msg1.set_labels(['bar', 'answered', 'foo'])
+        key1 = self._box.add(msg1)
+        self.assert_(set(self._box.get_labels()) == set(['foo', 'bar']))
+        msg0.set_labels(['blah', 'filed'])
+        self._box[key0] = msg0
+        self.assert_(set(self._box.get_labels()) ==
+                     set(['foo', 'bar', 'blah']))
+        self._box.remove(key1)
+        self.assert_(set(self._box.get_labels()) == set(['blah']))
+
+
+class TestMessage(TestBase):
+
+    _factory = mailbox.Message      # Overridden by subclasses to reuse tests
+
+    def setUp(self):
+        self._path = test_support.TESTFN
+
+    def tearDown(self):
+        self._delete_recursively(self._path)
+
+    def test_initialize_with_eMM(self):
+        # Initialize based on email.Message.Message instance
+        eMM = email.message_from_string(_sample_message)
+        msg = self._factory(eMM)
+        self._post_initialize_hook(msg)
+        self._check_sample(msg)
+
+    def test_initialize_with_string(self):
+        # Initialize based on string
+        msg = self._factory(_sample_message)
+        self._post_initialize_hook(msg)
+        self._check_sample(msg)
+
+    def test_initialize_with_file(self):
+        # Initialize based on contents of file
+        f = open(self._path, 'w+')
+        f.write(_sample_message)
+        f.seek(0)
+        msg = self._factory(f)
+        self._post_initialize_hook(msg)
+        self._check_sample(msg)
+        f.close()
+
+    def test_initialize_with_nothing(self):
+        # Initialize without arguments
+        msg = self._factory()
+        self._post_initialize_hook(msg)
+        self.assert_(isinstance(msg, email.Message.Message))
+        self.assert_(isinstance(msg, mailbox.Message))
+        self.assert_(isinstance(msg, self._factory))
+        self.assert_(msg.keys() == [])
+        self.assert_(not msg.is_multipart())
+        self.assert_(msg.get_payload() == None)
+
+    def test_initialize_incorrectly(self):
+        # Initialize with invalid argument
+        self.assertRaises(TypeError, lambda: self._factory(object()))
+
+    def test_become_message(self):
+        # Take on the state of another message
+        eMM = email.message_from_string(_sample_message)
+        msg = self._factory()
+        msg._become_message(eMM)
+        self._check_sample(msg)
+
+    def test_explain_to(self):
+        # Copy self's format-specific data to other message formats.
+        # This test is superficial; better ones are in TestMessageConversion.
+        msg = self._factory()
+        for class_ in (mailbox.Message, mailbox.MaildirMessage,
+                       mailbox.mboxMessage, mailbox.MHMessage,
+                       mailbox.BabylMessage, mailbox.MMDFMessage):
+            other_msg = class_()
+            msg._explain_to(other_msg)
+        other_msg = email.Message.Message()
+        self.assertRaises(TypeError, lambda: msg._explain_to(other_msg))
+
+    def _post_initialize_hook(self, msg):
+        # Overridden by subclasses to check extra things after initialization
+        pass
+
+
+class TestMaildirMessage(TestMessage):
+
+    _factory = mailbox.MaildirMessage
+
+    def _post_initialize_hook(self, msg):
+        self.assert_(msg._subdir == 'new')
+        self.assert_(msg._info == '')
+
+    def test_subdir(self):
+        # Use get_subdir() and set_subdir()
+        msg = mailbox.MaildirMessage(_sample_message)
+        self.assert_(msg.get_subdir() == 'new')
+        msg.set_subdir('cur')
+        self.assert_(msg.get_subdir() == 'cur')
+        msg.set_subdir('new')
+        self.assert_(msg.get_subdir() == 'new')
+        self.assertRaises(ValueError, lambda: msg.set_subdir('tmp'))
+        self.assert_(msg.get_subdir() == 'new')
+        msg.set_subdir('new')
+        self.assert_(msg.get_subdir() == 'new')
+        self._check_sample(msg)
+
+    def test_flags(self):
+        # Use get_flags(), set_flags(), add_flag(), remove_flag()
+        msg = mailbox.MaildirMessage(_sample_message)
+        self.assert_(msg.get_flags() == '')
+        self.assert_(msg.get_subdir() == 'new')
+        msg.set_flags('F')
+        self.assert_(msg.get_subdir() == 'new')
+        self.assert_(msg.get_flags() == 'F')
+        msg.set_flags('SDTP')
+        self.assert_(msg.get_flags() == 'DPST')
+        msg.add_flag('FT')
+        self.assert_(msg.get_flags() == 'DFPST')
+        msg.remove_flag('TDRP')
+        self.assert_(msg.get_flags() == 'FS')
+        self.assert_(msg.get_subdir() == 'new')
+        self._check_sample(msg)
+
+    def test_date(self):
+        # Use get_date() and set_date()
+        msg = mailbox.MaildirMessage(_sample_message)
+        self.assert_(abs(msg.get_date() - time.time()) < 60)
+        msg.set_date(0.0)
+        self.assert_(msg.get_date() == 0.0)
+
+    def test_info(self):
+        # Use get_info() and set_info()
+        msg = mailbox.MaildirMessage(_sample_message)
+        self.assert_(msg.get_info() == '')
+        msg.set_info('1,foo=bar')
+        self.assert_(msg.get_info() == '1,foo=bar')
+        self.assertRaises(TypeError, lambda: msg.set_info(None))
+        self._check_sample(msg)
+
+    def test_info_and_flags(self):
+        # Test interaction of info and flag methods
+        msg = mailbox.MaildirMessage(_sample_message)
+        self.assert_(msg.get_info() == '')
+        msg.set_flags('SF')
+        self.assert_(msg.get_flags() == 'FS')
+        self.assert_(msg.get_info() == '2,FS')
+        msg.set_info('1,')
+        self.assert_(msg.get_flags() == '')
+        self.assert_(msg.get_info() == '1,')
+        msg.remove_flag('RPT')
+        self.assert_(msg.get_flags() == '')
+        self.assert_(msg.get_info() == '1,')
+        msg.add_flag('D')
+        self.assert_(msg.get_flags() == 'D')
+        self.assert_(msg.get_info() == '2,D')
+        self._check_sample(msg)
+
+
+class _TestMboxMMDFMessage(TestMessage):
+
+    _factory = mailbox._mboxMMDFMessage
+
+    def _post_initialize_hook(self, msg):
+        self._check_from(msg)
+
+    def test_initialize_with_unixfrom(self):
+        # Initialize with a message that already has a _unixfrom attribute
+        msg = mailbox.Message(_sample_message)
+        msg.set_unixfrom('From foo@bar blah')
+        msg = mailbox.mboxMessage(msg)
+        self.assert_(msg.get_from() == 'foo@bar blah', msg.get_from())
+
+    def test_from(self):
+        # Get and set "From " line
+        msg = mailbox.mboxMessage(_sample_message)
+        self._check_from(msg)
+        msg.set_from('foo bar')
+        self.assert_(msg.get_from() == 'foo bar')
+        msg.set_from('foo@bar', True)
+        self._check_from(msg, 'foo@bar')
+        msg.set_from('blah@temp', time.localtime())
+        self._check_from(msg, 'blah@temp')
+
+    def test_flags(self):
+        # Use get_flags(), set_flags(), add_flag(), remove_flag()
+        msg = mailbox.mboxMessage(_sample_message)
+        self.assert_(msg.get_flags() == '')
+        msg.set_flags('F')
+        self.assert_(msg.get_flags() == 'F')
+        msg.set_flags('XODR')
+        self.assert_(msg.get_flags() == 'RODX')
+        msg.add_flag('FA')
+        self.assert_(msg.get_flags() == 'RODFAX')
+        msg.remove_flag('FDXA')
+        self.assert_(msg.get_flags() == 'RO')
+        self._check_sample(msg)
+
+    def _check_from(self, msg, sender=None):
+        # Check contents of "From " line
+        if sender is None:
+            sender = "MAILER-DAEMON"
+        self.assert_(re.match(sender + r" \w{3} \w{3} [\d ]\d [\d ]\d:\d{2}:"
+                              r"\d{2} \d{4}", msg.get_from()) is not None)
+
+
+class TestMboxMessage(_TestMboxMMDFMessage):
+
+    _factory = mailbox.mboxMessage
+
+
+class TestMHMessage(TestMessage):
+
+    _factory = mailbox.MHMessage
+
+    def _post_initialize_hook(self, msg):
+        self.assert_(msg._sequences == [])
+
+    def test_sequences(self):
+        # Get, set, join, and leave sequences
+        msg = mailbox.MHMessage(_sample_message)
+        self.assert_(msg.get_sequences() == [])
+        msg.set_sequences(['foobar'])
+        self.assert_(msg.get_sequences() == ['foobar'])
+        msg.set_sequences([])
+        self.assert_(msg.get_sequences() == [])
+        msg.add_sequence('unseen')
+        self.assert_(msg.get_sequences() == ['unseen'])
+        msg.add_sequence('flagged')
+        self.assert_(msg.get_sequences() == ['unseen', 'flagged'])
+        msg.add_sequence('flagged')
+        self.assert_(msg.get_sequences() == ['unseen', 'flagged'])
+        msg.remove_sequence('unseen')
+        self.assert_(msg.get_sequences() == ['flagged'])
+        msg.add_sequence('foobar')
+        self.assert_(msg.get_sequences() == ['flagged', 'foobar'])
+        msg.remove_sequence('replied')
+        self.assert_(msg.get_sequences() == ['flagged', 'foobar'])
+        msg.set_sequences(['foobar', 'replied'])
+        self.assert_(msg.get_sequences() == ['foobar', 'replied'])
+
+
+class TestBabylMessage(TestMessage):
+
+    _factory = mailbox.BabylMessage
+
+    def _post_initialize_hook(self, msg):
+        self.assert_(msg._labels == [])
+
+    def test_labels(self):
+        # Get, set, join, and leave labels
+        msg = mailbox.BabylMessage(_sample_message)
+        self.assert_(msg.get_labels() == [])
+        msg.set_labels(['foobar'])
+        self.assert_(msg.get_labels() == ['foobar'])
+        msg.set_labels([])
+        self.assert_(msg.get_labels() == [])
+        msg.add_label('filed')
+        self.assert_(msg.get_labels() == ['filed'])
+        msg.add_label('resent')
+        self.assert_(msg.get_labels() == ['filed', 'resent'])
+        msg.add_label('resent')
+        self.assert_(msg.get_labels() == ['filed', 'resent'])
+        msg.remove_label('filed')
+        self.assert_(msg.get_labels() == ['resent'])
+        msg.add_label('foobar')
+        self.assert_(msg.get_labels() == ['resent', 'foobar'])
+        msg.remove_label('unseen')
+        self.assert_(msg.get_labels() == ['resent', 'foobar'])
+        msg.set_labels(['foobar', 'answered'])
+        self.assert_(msg.get_labels() == ['foobar', 'answered'])
+
+    def test_visible(self):
+        # Get, set, and update visible headers
+        msg = mailbox.BabylMessage(_sample_message)
+        visible = msg.get_visible()
+        self.assert_(visible.keys() == [])
+        self.assert_(visible.get_payload() is None)
+        visible['User-Agent'] = 'FooBar 1.0'
+        visible['X-Whatever'] = 'Blah'
+        self.assert_(msg.get_visible().keys() == [])
+        msg.set_visible(visible)
+        visible = msg.get_visible()
+        self.assert_(visible.keys() == ['User-Agent', 'X-Whatever'])
+        self.assert_(visible['User-Agent'] == 'FooBar 1.0')
+        self.assert_(visible['X-Whatever'] == 'Blah')
+        self.assert_(visible.get_payload() is None)
+        msg.update_visible()
+        self.assert_(visible.keys() == ['User-Agent', 'X-Whatever'])
+        self.assert_(visible.get_payload() is None)
+        visible = msg.get_visible()
+        self.assert_(visible.keys() == ['User-Agent', 'Date', 'From', 'To',
+                                        'Subject'])
+        for header in ('User-Agent', 'Date', 'From', 'To', 'Subject'):
+            self.assert_(visible[header] == msg[header])
+
+
+class TestMMDFMessage(_TestMboxMMDFMessage):
+
+    _factory = mailbox.MMDFMessage
+
+
+class TestMessageConversion(TestBase):
+
+    def test_plain_to_x(self):
+        # Convert Message to all formats
+        for class_ in (mailbox.Message, mailbox.MaildirMessage,
+                       mailbox.mboxMessage, mailbox.MHMessage,
+                       mailbox.BabylMessage, mailbox.MMDFMessage):
+            msg_plain = mailbox.Message(_sample_message)
+            msg = class_(msg_plain)
+            self._check_sample(msg)
+
+    def test_x_to_plain(self):
+        # Convert all formats to Message
+        for class_ in (mailbox.Message, mailbox.MaildirMessage,
+                       mailbox.mboxMessage, mailbox.MHMessage,
+                       mailbox.BabylMessage, mailbox.MMDFMessage):
+            msg = class_(_sample_message)
+            msg_plain = mailbox.Message(msg)
+            self._check_sample(msg_plain)
+
+    def test_x_to_invalid(self):
+        # Convert all formats to an invalid format
+        for class_ in (mailbox.Message, mailbox.MaildirMessage,
+                       mailbox.mboxMessage, mailbox.MHMessage,
+                       mailbox.BabylMessage, mailbox.MMDFMessage):
+            self.assertRaises(TypeError, lambda: class_(False))
+
+    def test_maildir_to_maildir(self):
+        # Convert MaildirMessage to MaildirMessage
+        msg_maildir = mailbox.MaildirMessage(_sample_message)
+        msg_maildir.set_flags('DFPRST')
+        msg_maildir.set_subdir('cur')
+        date = msg_maildir.get_date()
+        msg = mailbox.MaildirMessage(msg_maildir)
+        self._check_sample(msg)
+        self.assert_(msg.get_flags() == 'DFPRST')
+        self.assert_(msg.get_subdir() == 'cur')
+        self.assert_(msg.get_date() == date)
+
+    def test_maildir_to_mboxmmdf(self):
+        # Convert MaildirMessage to mboxmessage and MMDFMessage
+        pairs = (('D', ''), ('F', 'F'), ('P', ''), ('R', 'A'), ('S', 'R'),
+                 ('T', 'D'), ('DFPRST', 'RDFA'))
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg_maildir = mailbox.MaildirMessage(_sample_message)
+            msg_maildir.set_date(0.0)
+            for setting, result in pairs:
+                msg_maildir.set_flags(setting)
+                msg = class_(msg_maildir)
+                self.assert_(msg.get_flags() == result)
+                self.assert_(msg.get_from() == 'MAILER-DAEMON %s' %
+                             time.asctime(time.gmtime(0.0)))
+            msg_maildir.set_subdir('cur')
+            self.assert_(class_(msg_maildir).get_flags() == 'RODFA')
+
+    def test_maildir_to_mh(self):
+        # Convert MaildirMessage to MHMessage
+        msg_maildir = mailbox.MaildirMessage(_sample_message)
+        pairs = (('D', ['unseen']), ('F', ['unseen', 'flagged']),
+                 ('P', ['unseen']), ('R', ['unseen', 'replied']), ('S', []),
+                 ('T', ['unseen']), ('DFPRST', ['replied', 'flagged']))
+        for setting, result in pairs:
+            msg_maildir.set_flags(setting)
+            self.assert_(mailbox.MHMessage(msg_maildir).get_sequences() == \
+                         result)
+
+    def test_maildir_to_babyl(self):
+        # Convert MaildirMessage to Babyl
+        msg_maildir = mailbox.MaildirMessage(_sample_message)
+        pairs = (('D', ['unseen']), ('F', ['unseen']),
+                 ('P', ['unseen', 'forwarded']), ('R', ['unseen', 'answered']),
+                 ('S', []), ('T', ['unseen', 'deleted']),
+                 ('DFPRST', ['deleted', 'answered', 'forwarded']))
+        for setting, result in pairs:
+            msg_maildir.set_flags(setting)
+            self.assert_(mailbox.BabylMessage(msg_maildir).get_labels() == \
+                         result)
+
+    def test_mboxmmdf_to_maildir(self):
+        # Convert mboxMessage and MMDFMessage to MaildirMessage
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg_mboxMMDF = class_(_sample_message)
+            msg_mboxMMDF.set_from('foo@bar', time.gmtime(0.0))
+            pairs = (('R', 'S'), ('O', ''), ('D', 'T'), ('F', 'F'), ('A', 'R'),
+                     ('RODFA', 'FRST'))
+            for setting, result in pairs:
+                msg_mboxMMDF.set_flags(setting)
+                msg = mailbox.MaildirMessage(msg_mboxMMDF)
+                self.assert_(msg.get_flags() == result)
+                self.assert_(msg.get_date() == 0.0, msg.get_date())
+            msg_mboxMMDF.set_flags('O')
+            self.assert_(mailbox.MaildirMessage(msg_mboxMMDF).get_subdir() == \
+                         'cur')
+
+    def test_mboxmmdf_to_mboxmmdf(self):
+        # Convert mboxMessage and MMDFMessage to mboxMessage and MMDFMessage
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg_mboxMMDF = class_(_sample_message)
+            msg_mboxMMDF.set_flags('RODFA')
+            msg_mboxMMDF.set_from('foo@bar')
+            for class2_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+                msg2 = class2_(msg_mboxMMDF)
+                self.assert_(msg2.get_flags() == 'RODFA')
+                self.assert_(msg2.get_from() == 'foo@bar')
+
+    def test_mboxmmdf_to_mh(self):
+        # Convert mboxMessage and MMDFMessage to MHMessage
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg_mboxMMDF = class_(_sample_message)
+            pairs = (('R', []), ('O', ['unseen']), ('D', ['unseen']),
+                     ('F', ['unseen', 'flagged']),
+                     ('A', ['unseen', 'replied']),
+                     ('RODFA', ['replied', 'flagged']))
+            for setting, result in pairs:
+                msg_mboxMMDF.set_flags(setting)
+                self.assert_(mailbox.MHMessage(msg_mboxMMDF).get_sequences() \
+                             == result)
+
+    def test_mboxmmdf_to_babyl(self):
+        # Convert mboxMessage and MMDFMessage to BabylMessage
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            msg = class_(_sample_message)
+            pairs = (('R', []), ('O', ['unseen']),
+                     ('D', ['unseen', 'deleted']), ('F', ['unseen']),
+                     ('A', ['unseen', 'answered']),
+                     ('RODFA', ['deleted', 'answered']))
+            for setting, result in pairs:
+                msg.set_flags(setting)
+                self.assert_(mailbox.BabylMessage(msg).get_labels() == result)
+
+    def test_mh_to_maildir(self):
+        # Convert MHMessage to MaildirMessage
+        pairs = (('unseen', ''), ('replied', 'RS'), ('flagged', 'FS'))
+        for setting, result in pairs:
+            msg = mailbox.MHMessage(_sample_message)
+            msg.add_sequence(setting)
+            self.assert_(mailbox.MaildirMessage(msg).get_flags() == result)
+            self.assert_(mailbox.MaildirMessage(msg).get_subdir() == 'cur')
+        msg = mailbox.MHMessage(_sample_message)
+        msg.add_sequence('unseen')
+        msg.add_sequence('replied')
+        msg.add_sequence('flagged')
+        self.assert_(mailbox.MaildirMessage(msg).get_flags() == 'FR')
+        self.assert_(mailbox.MaildirMessage(msg).get_subdir() == 'cur')
+
+    def test_mh_to_mboxmmdf(self):
+        # Convert MHMessage to mboxMessage and MMDFMessage
+        pairs = (('unseen', 'O'), ('replied', 'ROA'), ('flagged', 'ROF'))
+        for setting, result in pairs:
+            msg = mailbox.MHMessage(_sample_message)
+            msg.add_sequence(setting)
+            for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+                self.assert_(class_(msg).get_flags() == result)
+        msg = mailbox.MHMessage(_sample_message)
+        msg.add_sequence('unseen')
+        msg.add_sequence('replied')
+        msg.add_sequence('flagged')
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            self.assert_(class_(msg).get_flags() == 'OFA')
+
+    def test_mh_to_mh(self):
+        # Convert MHMessage to MHMessage
+        msg = mailbox.MHMessage(_sample_message)
+        msg.add_sequence('unseen')
+        msg.add_sequence('replied')
+        msg.add_sequence('flagged')
+        self.assert_(mailbox.MHMessage(msg).get_sequences() == \
+                     ['unseen', 'replied', 'flagged'])
+
+    def test_mh_to_babyl(self):
+        # Convert MHMessage to BabylMessage
+        pairs = (('unseen', ['unseen']), ('replied', ['answered']),
+                 ('flagged', []))
+        for setting, result in pairs:
+            msg = mailbox.MHMessage(_sample_message)
+            msg.add_sequence(setting)
+            self.assert_(mailbox.BabylMessage(msg).get_labels() == result)
+        msg = mailbox.MHMessage(_sample_message)
+        msg.add_sequence('unseen')
+        msg.add_sequence('replied')
+        msg.add_sequence('flagged')
+        self.assert_(mailbox.BabylMessage(msg).get_labels() == \
+                     ['unseen', 'answered'])
+
+    def test_babyl_to_maildir(self):
+        # Convert BabylMessage to MaildirMessage
+        pairs = (('unseen', ''), ('deleted', 'ST'), ('filed', 'S'),
+                 ('answered', 'RS'), ('forwarded', 'PS'), ('edited', 'S'),
+                 ('resent', 'PS'))
+        for setting, result in pairs:
+            msg = mailbox.BabylMessage(_sample_message)
+            msg.add_label(setting)
+            self.assert_(mailbox.MaildirMessage(msg).get_flags() == result)
+            self.assert_(mailbox.MaildirMessage(msg).get_subdir() == 'cur')
+        msg = mailbox.BabylMessage(_sample_message)
+        for label in ('unseen', 'deleted', 'filed', 'answered', 'forwarded',
+                      'edited', 'resent'):
+            msg.add_label(label)
+        self.assert_(mailbox.MaildirMessage(msg).get_flags() == 'PRT')
+        self.assert_(mailbox.MaildirMessage(msg).get_subdir() == 'cur')
+
+    def test_babyl_to_mboxmmdf(self):
+        # Convert BabylMessage to mboxMessage and MMDFMessage
+        pairs = (('unseen', 'O'), ('deleted', 'ROD'), ('filed', 'RO'),
+                 ('answered', 'ROA'), ('forwarded', 'RO'), ('edited', 'RO'),
+                 ('resent', 'RO'))
+        for setting, result in pairs:
+            for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+                msg = mailbox.BabylMessage(_sample_message)
+                msg.add_label(setting)
+                self.assert_(class_(msg).get_flags() == result)
+        msg = mailbox.BabylMessage(_sample_message)
+        for label in ('unseen', 'deleted', 'filed', 'answered', 'forwarded',
+                      'edited', 'resent'):
+            msg.add_label(label)
+        for class_ in (mailbox.mboxMessage, mailbox.MMDFMessage):
+            self.assert_(class_(msg).get_flags() == 'ODA')
+
+    def test_babyl_to_mh(self):
+        # Convert BabylMessage to MHMessage
+        pairs = (('unseen', ['unseen']), ('deleted', []), ('filed', []),
+                 ('answered', ['replied']), ('forwarded', []), ('edited', []),
+                 ('resent', []))
+        for setting, result in pairs:
+            msg = mailbox.BabylMessage(_sample_message)
+            msg.add_label(setting)
+            self.assert_(mailbox.MHMessage(msg).get_sequences() == result)
+        msg = mailbox.BabylMessage(_sample_message)
+        for label in ('unseen', 'deleted', 'filed', 'answered', 'forwarded',
+                      'edited', 'resent'):
+            msg.add_label(label)
+        self.assert_(mailbox.MHMessage(msg).get_sequences() == \
+                     ['unseen', 'replied'])
+
+    def test_babyl_to_babyl(self):
+        # Convert BabylMessage to BabylMessage
+        msg = mailbox.BabylMessage(_sample_message)
+        msg.update_visible()
+        for label in ('unseen', 'deleted', 'filed', 'answered', 'forwarded',
+                      'edited', 'resent'):
+            msg.add_label(label)       
+        msg2 = mailbox.BabylMessage(msg)
+        self.assert_(msg2.get_labels() == ['unseen', 'deleted', 'filed',
+                                           'answered', 'forwarded', 'edited',
+                                           'resent'])
+        self.assert_(msg.get_visible().keys() == msg2.get_visible().keys())
+        for key in msg.get_visible().keys():
+            self.assert_(msg.get_visible()[key] == msg2.get_visible()[key])
+
+
+class TestProxyFileBase(TestBase):
+
+    def _test_read(self, proxy):
+        # Read by byte
+        proxy.seek(0)
+        self.assert_(proxy.read() == 'bar')
+        proxy.seek(1)
+        self.assert_(proxy.read() == 'ar')
+        proxy.seek(0)
+        self.assert_(proxy.read(2) == 'ba')
+        proxy.seek(1)
+        self.assert_(proxy.read(-1) == 'ar')
+        proxy.seek(2)
+        self.assert_(proxy.read(1000) == 'r')
+
+    def _test_readline(self, proxy):
+        # Read by line
+        proxy.seek(0)
+        self.assert_(proxy.readline() == 'foo' + os.linesep)
+        self.assert_(proxy.readline() == 'bar' + os.linesep)
+        self.assert_(proxy.readline() == 'fred' + os.linesep)
+        self.assert_(proxy.readline() == 'bob')
+        proxy.seek(2)
+        self.assert_(proxy.readline() == 'o' + os.linesep)
+        proxy.seek(6 + 2 * len(os.linesep))
+        self.assert_(proxy.readline() == 'fred' + os.linesep)
+        proxy.seek(6 + 2 * len(os.linesep))
+        self.assert_(proxy.readline(2) == 'fr')
+        self.assert_(proxy.readline(-10) == 'ed' + os.linesep)
+
+    def _test_readlines(self, proxy):
+        # Read multiple lines
+        proxy.seek(0)
+        self.assert_(proxy.readlines() == ['foo' + os.linesep,
+                                           'bar' + os.linesep,
+                                           'fred' + os.linesep, 'bob'])
+        proxy.seek(0)
+        self.assert_(proxy.readlines(2) == ['foo' + os.linesep])
+        proxy.seek(3 + len(os.linesep))
+        self.assert_(proxy.readlines(4 + len(os.linesep)) ==
+                     ['bar' + os.linesep, 'fred' + os.linesep])
+        proxy.seek(3)
+        self.assert_(proxy.readlines(1000) == [os.linesep, 'bar' + os.linesep,
+                                               'fred' + os.linesep, 'bob'])
+
+    def _test_iteration(self, proxy):
+        # Iterate by line
+        proxy.seek(0)
+        iterator = iter(proxy)
+        self.assert_(iterator.next() == 'foo' + os.linesep)
+        self.assert_(iterator.next() == 'bar' + os.linesep)
+        self.assert_(iterator.next() == 'fred' + os.linesep)
+        self.assert_(iterator.next() == 'bob')
+        self.assertRaises(StopIteration, lambda: iterator.next())
+
+    def _test_seek_and_tell(self, proxy):
+        # Seek and use tell to check position
+        proxy.seek(3)
+        self.assert_(proxy.tell() == 3)
+        self.assert_(proxy.read(len(os.linesep)) == os.linesep)
+        proxy.seek(2, 1)
+        self.assert_(proxy.read(1 + len(os.linesep)) == 'r' + os.linesep)
+        proxy.seek(-3 - len(os.linesep), 2)
+        self.assert_(proxy.read(3) == 'bar')
+        proxy.seek(2, 0)
+        self.assert_(proxy.read() == 'o' + os.linesep + 'bar' + os.linesep)
+        proxy.seek(100)
+        self.assert_(proxy.read() == '')
+
+    def _test_close(self, proxy):
+        # Close a file
+        proxy.close()
+        self.assertRaises(AttributeError, lambda: proxy.close())
+
+
+class TestProxyFile(TestProxyFileBase):
+
+    def setUp(self):
+        self._path = test_support.TESTFN
+        self._file = file(self._path, 'wb+')
+
+    def tearDown(self):
+        self._file.close()
+        self._delete_recursively(self._path)
+
+    def test_initialize(self):
+        # Initialize and check position
+        self._file.write('foo')
+        pos = self._file.tell()
+        proxy0 = mailbox._ProxyFile(self._file)
+        self.assert_(proxy0.tell() == pos)
+        self.assert_(self._file.tell() == pos)
+        proxy1 = mailbox._ProxyFile(self._file, 0)
+        self.assert_(proxy1.tell() == 0)
+        self.assert_(self._file.tell() == pos)
+
+    def test_read(self):
+        self._file.write('bar')
+        self._test_read(mailbox._ProxyFile(self._file))
+
+    def test_readline(self):
+        self._file.write('foo%sbar%sfred%sbob' % (os.linesep, os.linesep,
+                                                  os.linesep))
+        self._test_readline(mailbox._ProxyFile(self._file))
+
+    def test_readlines(self):
+        self._file.write('foo%sbar%sfred%sbob' % (os.linesep, os.linesep,
+                                                  os.linesep))
+        self._test_readlines(mailbox._ProxyFile(self._file))
+
+    def test_iteration(self):
+        self._file.write('foo%sbar%sfred%sbob' % (os.linesep, os.linesep,
+                                                  os.linesep))
+        self._test_iteration(mailbox._ProxyFile(self._file))
+
+    def test_seek_and_tell(self):
+        self._file.write('foo%sbar%s' % (os.linesep, os.linesep))
+        self._test_seek_and_tell(mailbox._ProxyFile(self._file))
+
+    def test_close(self):
+        self._file.write('foo%sbar%s' % (os.linesep, os.linesep))
+        self._test_close(mailbox._ProxyFile(self._file))
+
+
+class TestPartialFile(TestProxyFileBase):
+
+    def setUp(self):
+        self._path = test_support.TESTFN
+        self._file = file(self._path, 'wb+')
+
+    def tearDown(self):
+        self._file.close()
+        self._delete_recursively(self._path)
+
+    def test_initialize(self):
+        # Initialize and check position
+        self._file.write('foo' + os.linesep + 'bar')
+        pos = self._file.tell()
+        proxy = mailbox._PartialFile(self._file, 2, 5)
+        self.assert_(proxy.tell() == 0)
+        self.assert_(self._file.tell() == pos)
+
+    def test_read(self):
+        self._file.write('***bar***')
+        self._test_read(mailbox._PartialFile(self._file, 3, 6))
+
+    def test_readline(self):
+        self._file.write('!!!!!foo%sbar%sfred%sbob!!!!!' %
+                         (os.linesep, os.linesep, os.linesep))
+        self._test_readline(mailbox._PartialFile(self._file, 5,
+                                                 18 + 3 * len(os.linesep)))
+
+    def test_readlines(self):
+        self._file.write('foo%sbar%sfred%sbob?????' %
+                         (os.linesep, os.linesep, os.linesep))
+        self._test_readlines(mailbox._PartialFile(self._file, 0,
+                                                  13 + 3 * len(os.linesep)))
+
+    def test_iteration(self):
+        self._file.write('____foo%sbar%sfred%sbob####' %
+                         (os.linesep, os.linesep, os.linesep))
+        self._test_iteration(mailbox._PartialFile(self._file, 4,
+                                                  17 + 3 * len(os.linesep)))
+
+    def test_seek_and_tell(self):
+        self._file.write('(((foo%sbar%s$$$' % (os.linesep, os.linesep))
+        self._test_seek_and_tell(mailbox._PartialFile(self._file, 3,
+                                                      9 + 2 * len(os.linesep)))
+
+    def test_close(self):
+        self._file.write('&foo%sbar%s^' % (os.linesep, os.linesep))
+        self._test_close(mailbox._PartialFile(self._file, 1,
+                                              6 + 3 * len(os.linesep)))
+
+
+## Start: tests from the original module (for backward compatibility).
+
 FROM_ = "From some.body@dummy.domain  Sat Jul 24 13:43:35 2004\n"
 DUMMY_MESSAGE = """\
 From: some.body@dummy.domain
@@ -65,15 +1622,15 @@ class MaildirTestCase(unittest.TestCase):
         # Test for regression on bug #117490:
         # Make sure the boxes attribute actually gets set.
         self.mbox = mailbox.Maildir(test_support.TESTFN)
-        self.assert_(hasattr(self.mbox, "boxes"))
-        self.assert_(len(self.mbox.boxes) == 0)
+        #self.assert_(hasattr(self.mbox, "boxes"))
+        #self.assert_(len(self.mbox.boxes) == 0)
         self.assert_(self.mbox.next() is None)
         self.assert_(self.mbox.next() is None)
 
     def test_nonempty_maildir_cur(self):
         self.createMessage("cur")
         self.mbox = mailbox.Maildir(test_support.TESTFN)
-        self.assert_(len(self.mbox.boxes) == 1)
+        #self.assert_(len(self.mbox.boxes) == 1)
         self.assert_(self.mbox.next() is not None)
         self.assert_(self.mbox.next() is None)
         self.assert_(self.mbox.next() is None)
@@ -81,7 +1638,7 @@ class MaildirTestCase(unittest.TestCase):
     def test_nonempty_maildir_new(self):
         self.createMessage("new")
         self.mbox = mailbox.Maildir(test_support.TESTFN)
-        self.assert_(len(self.mbox.boxes) == 1)
+        #self.assert_(len(self.mbox.boxes) == 1)
         self.assert_(self.mbox.next() is not None)
         self.assert_(self.mbox.next() is None)
         self.assert_(self.mbox.next() is None)
@@ -90,7 +1647,7 @@ class MaildirTestCase(unittest.TestCase):
         self.createMessage("cur")
         self.createMessage("new")
         self.mbox = mailbox.Maildir(test_support.TESTFN)
-        self.assert_(len(self.mbox.boxes) == 2)
+        #self.assert_(len(self.mbox.boxes) == 2)
         self.assert_(self.mbox.next() is not None)
         self.assert_(self.mbox.next() is not None)
         self.assert_(self.mbox.next() is None)
@@ -108,12 +1665,99 @@ class MaildirTestCase(unittest.TestCase):
             self.assertEqual(len(str(msg)), len(FROM_)+len(DUMMY_MESSAGE))
         self.assertEqual(n, 1)
 
-    # XXX We still need more tests!
+## End: classes from the original module (for backward compatibility).
+
+
+_sample_message = """\
+Return-Path: <gkj@gregorykjohnson.com>
+X-Original-To: gkj+person@localhost
+Delivered-To: gkj+person@localhost
+Received: from localhost (localhost [127.0.0.1])
+	by andy.gregorykjohnson.com (Postfix) with ESMTP id 356ED9DD17
+	for <gkj+person@localhost>; Wed, 13 Jul 2005 17:23:16 -0400 (EDT)
+Delivered-To: gkj@sundance.gregorykjohnson.com
+Received: from localhost [127.0.0.1]
+	by localhost with POP3 (fetchmail-6.2.5)
+	for gkj+person@localhost (single-drop); Wed, 13 Jul 2005 17:23:16 -0400 (EDT)
+Received: from andy.gregorykjohnson.com (andy.gregorykjohnson.com [64.32.235.228])
+	by sundance.gregorykjohnson.com (Postfix) with ESMTP id 5B056316746
+	for <gkj@gregorykjohnson.com>; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)
+Received: by andy.gregorykjohnson.com (Postfix, from userid 1000)
+	id 490CD9DD17; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)
+Date: Wed, 13 Jul 2005 17:23:11 -0400
+From: "Gregory K. Johnson" <gkj@gregorykjohnson.com>
+To: gkj@gregorykjohnson.com
+Subject: Sample message
+Message-ID: <20050713212311.GC4701@andy.gregorykjohnson.com>
+Mime-Version: 1.0
+Content-Type: multipart/mixed; boundary="NMuMz9nt05w80d4+"
+Content-Disposition: inline
+User-Agent: Mutt/1.5.9i
+
+
+--NMuMz9nt05w80d4+
+Content-Type: text/plain; charset=us-ascii
+Content-Disposition: inline
+
+This is a sample message.
+
+-- 
+Gregory K. Johnson
+
+--NMuMz9nt05w80d4+
+Content-Type: application/octet-stream
+Content-Disposition: attachment; filename="text.gz"
+Content-Transfer-Encoding: base64
+
+H4sICM2D1UIAA3RleHQAC8nILFYAokSFktSKEoW0zJxUPa7wzJIMhZLyfIWczLzUYj0uAHTs
+3FYlAAAA
+
+--NMuMz9nt05w80d4+--
+"""
+
+_sample_headers = {
+    "Return-Path":"<gkj@gregorykjohnson.com>",
+    "X-Original-To":"gkj+person@localhost",
+    "Delivered-To":"gkj+person@localhost",
+    "Received":"""from localhost (localhost [127.0.0.1])
+	by andy.gregorykjohnson.com (Postfix) with ESMTP id 356ED9DD17
+	for <gkj+person@localhost>; Wed, 13 Jul 2005 17:23:16 -0400 (EDT)""",
+    "Delivered-To":"gkj@sundance.gregorykjohnson.com",
+    "Received":"""from localhost [127.0.0.1]
+	by localhost with POP3 (fetchmail-6.2.5)
+	for gkj+person@localhost (single-drop); Wed, 13 Jul 2005 17:23:16 -0400 (EDT)""",
+    "Received":"""from andy.gregorykjohnson.com (andy.gregorykjohnson.com [64.32.235.228])
+	by sundance.gregorykjohnson.com (Postfix) with ESMTP id 5B056316746
+	for <gkj@gregorykjohnson.com>; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)""",
+    "Received":"""by andy.gregorykjohnson.com (Postfix, from userid 1000)
+	id 490CD9DD17; Wed, 13 Jul 2005 17:23:11 -0400 (EDT)""",
+    "Date":"Wed, 13 Jul 2005 17:23:11 -0400",
+    "From":""""Gregory K. Johnson" <gkj@gregorykjohnson.com>""",
+    "To":"gkj@gregorykjohnson.com",
+    "Subject":"Sample message",
+    "Mime-Version":"1.0",
+    "Content-Type":"""multipart/mixed; boundary="NMuMz9nt05w80d4+\"""",
+    "Content-Disposition":"inline",
+    "User-Agent": "Mutt/1.5.9i" }
+
+_sample_payloads = ("""This is a sample message.
+
+-- 
+Gregory K. Johnson
+""",
+"""H4sICM2D1UIAA3RleHQAC8nILFYAokSFktSKEoW0zJxUPa7wzJIMhZLyfIWczLzUYj0uAHTs
+3FYlAAAA
+""")
 
 
 def test_main():
-    test_support.run_unittest(MaildirTestCase)
+    tests = (TestMailboxSuperclass, TestMaildir, TestMbox, TestMMDF, TestMH,
+             TestBabyl, TestMessage, TestMaildirMessage, TestMboxMessage,
+             TestMHMessage, TestBabylMessage, TestMMDFMessage,
+             TestMessageConversion, TestProxyFile, TestPartialFile,
+             MaildirTestCase)
+    test_support.run_unittest(*tests)
 
 
-if __name__ == "__main__":
+if __name__ == '__main__':
     test_main()

Misc/ACKS

@@ -313,6 +313,7 @@ Drew Jenkins
 Flemming Kjr Jensen
 Jiba
 Orjan Johansen
+Gregory K. Johnson
 Simon Johnston
 Evan Jones
 Richard Jones

Misc/NEWS

@@ -99,6 +99,10 @@ Library
   as ``walk_packages()`` to support working with packages that are either
   in the filesystem or zip files.
 
+- The mailbox module can now modify and delete messages from
+  mailboxes, in addition to simply reading them.  Thanks to Gregory
+  K. Johnson for writing the code, and to the 2005 Google Summer of
+  Code for funding his work.
 
 - The ``__del__`` method of class ``local`` in module ``_threading_local``
   returned before accomplishing any of its intended cleanup.
@@ -202,8 +206,8 @@ Core and builtins
   especially long-running applications that, from time to time, temporarily
   use a large number of small objects.  Note that when Python returns an
   arena to the platform C's ``free()``, there's no guarantee that the
-  platform C will in turn return that memory to the operating system.  The
-  effect of the patch is to stop making that impossible, and in tests it
+  platform C library will in turn return that memory to the operating system.
+  The effect of the patch is to stop making that impossible, and in tests it
   appears to be effective at least on Microsoft C and gcc-based systems.
   Thanks to Evan Jones for hard work and patience.