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Commit 3cdb8f32 authored by Guido van Rossum's avatar Guido van Rossum
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Update the description and the example to the new functionality, which 

is mostly concentrated in a generalized find_module() and the new
load_module().  Added the new module type constants.  Declare that
SEARCH_ERROR and a whole bunch of module-type-specific functions are
obsolete.
parent 4ece95d5
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Doc/lib/libimp.tex
View file @ 3cdb8f32
......@@ -11,31 +11,124 @@ functions:
\begin{funcdesc}{get_magic}{}
Return the magic string value used to recognize byte-compiled code
files (``\code{.pyc} files'').
files (``\code{.pyc} files''). (This value may be different for each
Python version.)
\end{funcdesc}
\begin{funcdesc}{get_suffixes}{}
Return a list of triples, each describing a particular type of file.
Return a list of triples, each describing a particular type of module.
Each triple has the form \code{(\var{suffix}, \var{mode},
\var{type})}, where \var{suffix} is a string to be appended to the
module name to form the filename to search for, \var{mode} is the mode
string to pass to the built-in \code{open} function to open the file
(this can be \code{'r'} for text files or \code{'rb'} for binary
files), and \var{type} is the file type, which has one of the values
\code{PY_SOURCE}, \code{PY_COMPILED} or \code{C_EXTENSION}, defined
below. (System-dependent values may also be returned.)
\code{PY_SOURCE}, \code{PY_COMPILED}, or \code{C_EXTENSION}, defined
below.
\end{funcdesc}
\begin{funcdesc}{find_module}{name\, \optional{path}}
Try to find the module \var{name} on the search path \var{path}. The
default \var{path} is \code{sys.path}. The return value is a triple
Try to find the module \var{name} on the search path \var{path}. If
\var{path} is a list of directory names, each directory is searched
for files with any of the suffixes returned by \code{get_suffixes()}
above. Invalid names in the list are silently ignored (but all list
items must be strings). If \var{path} is omitted or \code{None}, the
list of directory names given by \code{sys.path} is searched, but
first it searches a few special places: it tries to find a built-in
module with the given name (\code{C_BUILTIN}), then a frozen module
(\code{PY_FROZEN}), and on some systems some other places are looked
in as well (on the Mac, it looks for a resource (\code{PY_RESOURCE});
on Windows, it looks in the registry which may point to a specific
file).
If search is successful, the return value is a triple
\code{(\var{file}, \var{pathname}, \var{description})} where
\var{file} is an open file object positioned at the beginning,
\var{pathname} is the pathname of the
file found, and \var{description} is a triple as contained in the list
returned by \code{get_suffixes} describing the kind of file found.
returned by \code{get_suffixes} describing the kind of module found.
If the module does not live in a file, the returned \var{file} is
\code{None}, \var{filename} is the empty string, and the
\var{description} tuple contains empty strings for its suffix and
mode; the module type is as indicate in parentheses dabove. If the
search is unsuccessful, \code{ImportError} is raised. Other
exceptions indicate problems with the arguments or environment.
This function does not handle hierarchical module names (names
containing dots). In order to find var{P}.\var{M}, i.e., submodule
\var{M} of package \var{P}, use \code{find_module()} and
\code{load_module()} to find and load package \var{P}, and then use
\code{find_module()} with the \var{path} argument set to
\code{\var{P}.__path__}. When \var{P} itself has a dotted name, apply
this recipe recursively.
\end{funcdesc}
\begin{funcdesc}{load_module}{name, file, filename, description}
Load a module that was previously found by \code{find_module()} (or by
an otherwise conducted search yielding compatible results). This
function does more than importing the module: if the module was
already imported, it is equivalent to a \code{reload()}! The
\var{name} argument indicates the full module name (including the
package name, if this is a submodule of a package). The \var{file}
argument is an open file, and \var{filename} is the corresponding
file name; these can be \code{None} and \code{""}, respectively, when
the module is not being loaded from a file. The \var{description}
argument is a tuple as returned by \code{find_module()} describing what
kind of module must be loaded.
If the load is successful, the return value is the module object;
otherwise, an exception (usually \code{ImportError}) is raised.
\strong{Important:} the caller is responsible for closing the
\var{file} argument, if it was not \code{None}, even when an exception
is raised. This is best done using a try-finally statement.
\end{funcdesc}
\begin{funcdesc}{new_module}{name}
Return a new empty module object called \var{name}. This object is
{\em not} inserted in \code{sys.modules}.
\end{funcdesc}
The following constants with integer values, defined in this module,
are used to indicate the search result of \code{find_module()}.
\begin{datadesc}{PY_SOURCE}
The module was found as a source file.
\end{datadesc}
\begin{datadesc}{PY_COMPILED}
The module was found as a compiled code object file.
\end{datadesc}
\begin{datadesc}{C_EXTENSION}
The module was found as dynamically loadable shared library.
\end{datadesc}
\begin{datadesc}{PY_RESOURCE}
The module was found as a Macintosh resource. This value can only be
returned on a Macintosh.
\end{datadesc}
\begin{datadesc}{PKG_DIRECTORY}
The module was found as a package directory.
\end{datadesc}
\begin{datadesc}{C_BUILTIN}
The module was found as a built-in module.
\end{datadesc}
\begin{datadesc}{PY_FROZEN}
The module was found as a frozen module (see \code{init_frozen}).
\end{datadesc}
The following constant and functions are obsolete; their functionality
is available through \code{find_module()} or \code{load_module()}.
They are kept around for backward compatibility:
\begin{datadesc}{SEARCH_ERROR}
Unused.
\end{datadesc}
\begin{funcdesc}{init_builtin}{name}
Initialize the built-in module called \var{name} and return its module
object. If the module was already initialized, it will be initialized
......@@ -106,70 +199,37 @@ properly matching byte-compiled file (with suffix \code{.pyc}) exists,
it will be used instead of parsing the given source file.
\end{funcdesc}
\begin{funcdesc}{new_module}{name}
Return a new empty module object called \var{name}. This object is
{\em not} inserted in \code{sys.modules}.
\end{funcdesc}
The following constants with integer values, defined in the module,
are used to indicate the search result of \code{imp.find_module}.
\begin{datadesc}{SEARCH_ERROR}
The module was not found.
\end{datadesc}
\begin{datadesc}{PY_SOURCE}
The module was found as a source file.
\end{datadesc}
\begin{datadesc}{PY_COMPILED}
The module was found as a compiled code object file.
\end{datadesc}
\begin{datadesc}{C_EXTENSION}
The module was found as dynamically loadable shared library.
\end{datadesc}
\subsection{Examples}
The following function emulates the default import statement:
The following function emulates what was the standard import statement
up to Python 1.4 (i.e., no hierarchical module names). (This
\emph{implementation} wouldn't work in that version, since
\code{imp.find_module()} has been extended and
\code{imp.load_module()} has been added in 1.4.)
\bcode\begin{verbatim}
import imp
import sys
import imp import sys
def __import__(name, globals=None, locals=None, fromlist=None):
# Fast path: see if the module has already been imported.
if sys.modules.has_key(name):
try:
return sys.modules[name]
except KeyError:
pass
# If any of the following calls raises an exception,
# there's a problem we can't handle -- let the caller handle it.
# See if it's a built-in module.
m = imp.init_builtin(name)
if m:
return m
# See if it's a frozen module.
m = imp.init_frozen(name)
if m:
return m
# Search the default path (i.e. sys.path).
fp, pathname, (suffix, mode, type) = imp.find_module(name)
# See what we got.
fp, pathname, description = imp.find_module(name)
try:
if type == imp.C_EXTENSION:
return imp.load_dynamic(name, pathname)
if type == imp.PY_SOURCE:
return imp.load_source(name, pathname, fp)
if type == imp.PY_COMPILED:
return imp.load_compiled(name, pathname, fp)
# Shouldn't get here at all.
raise ImportError, '%s: unknown module type (%d)' % (name, type)
return imp.load_module(name, fp, pathname, description)
finally:
# Since we may exit via an exception, close fp explicitly.
fp.close()
if fp:
fp.close()
\end{verbatim}\ecode
A more complete example that implements hierarchical module names and
includes a \code{reload()} function can be found in the standard
module \code{knee} (which is intended as an example only -- don't rely
on any part of it being a standard interface).
Doc/libimp.tex
View file @ 3cdb8f32
......@@ -11,31 +11,124 @@ functions:
\begin{funcdesc}{get_magic}{}
Return the magic string value used to recognize byte-compiled code
files (``\code{.pyc} files'').
files (``\code{.pyc} files''). (This value may be different for each
Python version.)
\end{funcdesc}
\begin{funcdesc}{get_suffixes}{}
Return a list of triples, each describing a particular type of file.
Return a list of triples, each describing a particular type of module.
Each triple has the form \code{(\var{suffix}, \var{mode},
\var{type})}, where \var{suffix} is a string to be appended to the
module name to form the filename to search for, \var{mode} is the mode
string to pass to the built-in \code{open} function to open the file
(this can be \code{'r'} for text files or \code{'rb'} for binary
files), and \var{type} is the file type, which has one of the values
\code{PY_SOURCE}, \code{PY_COMPILED} or \code{C_EXTENSION}, defined
below. (System-dependent values may also be returned.)
\code{PY_SOURCE}, \code{PY_COMPILED}, or \code{C_EXTENSION}, defined
below.
\end{funcdesc}
\begin{funcdesc}{find_module}{name\, \optional{path}}
Try to find the module \var{name} on the search path \var{path}. The
default \var{path} is \code{sys.path}. The return value is a triple
Try to find the module \var{name} on the search path \var{path}. If
\var{path} is a list of directory names, each directory is searched
for files with any of the suffixes returned by \code{get_suffixes()}
above. Invalid names in the list are silently ignored (but all list
items must be strings). If \var{path} is omitted or \code{None}, the
list of directory names given by \code{sys.path} is searched, but
first it searches a few special places: it tries to find a built-in
module with the given name (\code{C_BUILTIN}), then a frozen module
(\code{PY_FROZEN}), and on some systems some other places are looked
in as well (on the Mac, it looks for a resource (\code{PY_RESOURCE});
on Windows, it looks in the registry which may point to a specific
file).
If search is successful, the return value is a triple
\code{(\var{file}, \var{pathname}, \var{description})} where
\var{file} is an open file object positioned at the beginning,
\var{pathname} is the pathname of the
file found, and \var{description} is a triple as contained in the list
returned by \code{get_suffixes} describing the kind of file found.
returned by \code{get_suffixes} describing the kind of module found.
If the module does not live in a file, the returned \var{file} is
\code{None}, \var{filename} is the empty string, and the
\var{description} tuple contains empty strings for its suffix and
mode; the module type is as indicate in parentheses dabove. If the
search is unsuccessful, \code{ImportError} is raised. Other
exceptions indicate problems with the arguments or environment.
This function does not handle hierarchical module names (names
containing dots). In order to find var{P}.\var{M}, i.e., submodule
\var{M} of package \var{P}, use \code{find_module()} and
\code{load_module()} to find and load package \var{P}, and then use
\code{find_module()} with the \var{path} argument set to
\code{\var{P}.__path__}. When \var{P} itself has a dotted name, apply
this recipe recursively.
\end{funcdesc}
\begin{funcdesc}{load_module}{name, file, filename, description}
Load a module that was previously found by \code{find_module()} (or by
an otherwise conducted search yielding compatible results). This
function does more than importing the module: if the module was
already imported, it is equivalent to a \code{reload()}! The
\var{name} argument indicates the full module name (including the
package name, if this is a submodule of a package). The \var{file}
argument is an open file, and \var{filename} is the corresponding
file name; these can be \code{None} and \code{""}, respectively, when
the module is not being loaded from a file. The \var{description}
argument is a tuple as returned by \code{find_module()} describing what
kind of module must be loaded.
If the load is successful, the return value is the module object;
otherwise, an exception (usually \code{ImportError}) is raised.
\strong{Important:} the caller is responsible for closing the
\var{file} argument, if it was not \code{None}, even when an exception
is raised. This is best done using a try-finally statement.
\end{funcdesc}
\begin{funcdesc}{new_module}{name}
Return a new empty module object called \var{name}. This object is
{\em not} inserted in \code{sys.modules}.
\end{funcdesc}
The following constants with integer values, defined in this module,
are used to indicate the search result of \code{find_module()}.
\begin{datadesc}{PY_SOURCE}
The module was found as a source file.
\end{datadesc}
\begin{datadesc}{PY_COMPILED}
The module was found as a compiled code object file.
\end{datadesc}
\begin{datadesc}{C_EXTENSION}
The module was found as dynamically loadable shared library.
\end{datadesc}
\begin{datadesc}{PY_RESOURCE}
The module was found as a Macintosh resource. This value can only be
returned on a Macintosh.
\end{datadesc}
\begin{datadesc}{PKG_DIRECTORY}
The module was found as a package directory.
\end{datadesc}
\begin{datadesc}{C_BUILTIN}
The module was found as a built-in module.
\end{datadesc}
\begin{datadesc}{PY_FROZEN}
The module was found as a frozen module (see \code{init_frozen}).
\end{datadesc}
The following constant and functions are obsolete; their functionality
is available through \code{find_module()} or \code{load_module()}.
They are kept around for backward compatibility:
\begin{datadesc}{SEARCH_ERROR}
Unused.
\end{datadesc}
\begin{funcdesc}{init_builtin}{name}
Initialize the built-in module called \var{name} and return its module
object. If the module was already initialized, it will be initialized
......@@ -106,70 +199,37 @@ properly matching byte-compiled file (with suffix \code{.pyc}) exists,
it will be used instead of parsing the given source file.
\end{funcdesc}
\begin{funcdesc}{new_module}{name}
Return a new empty module object called \var{name}. This object is
{\em not} inserted in \code{sys.modules}.
\end{funcdesc}
The following constants with integer values, defined in the module,
are used to indicate the search result of \code{imp.find_module}.
\begin{datadesc}{SEARCH_ERROR}
The module was not found.
\end{datadesc}
\begin{datadesc}{PY_SOURCE}
The module was found as a source file.
\end{datadesc}
\begin{datadesc}{PY_COMPILED}
The module was found as a compiled code object file.
\end{datadesc}
\begin{datadesc}{C_EXTENSION}
The module was found as dynamically loadable shared library.
\end{datadesc}
\subsection{Examples}
The following function emulates the default import statement:
The following function emulates what was the standard import statement
up to Python 1.4 (i.e., no hierarchical module names). (This
\emph{implementation} wouldn't work in that version, since
\code{imp.find_module()} has been extended and
\code{imp.load_module()} has been added in 1.4.)
\bcode\begin{verbatim}
import imp
import sys
import imp import sys
def __import__(name, globals=None, locals=None, fromlist=None):
# Fast path: see if the module has already been imported.
if sys.modules.has_key(name):
try:
return sys.modules[name]
except KeyError:
pass
# If any of the following calls raises an exception,
# there's a problem we can't handle -- let the caller handle it.
# See if it's a built-in module.
m = imp.init_builtin(name)
if m:
return m
# See if it's a frozen module.
m = imp.init_frozen(name)
if m:
return m
# Search the default path (i.e. sys.path).
fp, pathname, (suffix, mode, type) = imp.find_module(name)
# See what we got.
fp, pathname, description = imp.find_module(name)
try:
if type == imp.C_EXTENSION:
return imp.load_dynamic(name, pathname)
if type == imp.PY_SOURCE:
return imp.load_source(name, pathname, fp)
if type == imp.PY_COMPILED:
return imp.load_compiled(name, pathname, fp)
# Shouldn't get here at all.
raise ImportError, '%s: unknown module type (%d)' % (name, type)
return imp.load_module(name, fp, pathname, description)
finally:
# Since we may exit via an exception, close fp explicitly.
fp.close()
if fp:
fp.close()
\end{verbatim}\ecode
A more complete example that implements hierarchical module names and
includes a \code{reload()} function can be found in the standard
module \code{knee} (which is intended as an example only -- don't rely
on any part of it being a standard interface).
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