Added a lot of new stuff to the debugging section.

Doc/lib/libdoctest.tex

@@ -1547,34 +1547,174 @@ initialized by the constructor, and should not be modified directly.
 
 \subsection{Debugging\label{doctest-debugging}}
 
-Doctest provides three mechanisms for debugging doctest examples:
+Doctest provides several mechanisms for debugging doctest examples:
 
-\begin{enumerate}
-\item The \function{debug()} function converts a specified doctest
-      to a Python script, and executes that script using \module{pdb}.
+\begin{itemize}
+\item Several functions convert doctests to executable Python
+      programs, which can be run under the Python debugger, \refmodule{pdb}.
 \item The \class{DebugRunner} class is a subclass of
       \class{DocTestRunner} that raises an exception for the first
       failing example, containing information about that example.
       This information can be used to perform post-mortem debugging on
       the example.
-\item The unittest cases generated by \function{DocTestSuite()}
-      support the \method{debug} method defined by
+\item The \module{unittest} cases generated by \function{DocTestSuite()}
+      support the \method{debug()} method defined by
       \class{unittest.TestCase}.
-\end{enumerate}
+\item You can add a call to \function{pdb.set_trace()} in a doctest
+      example, and you'll drop into the Python debugger when that
+      line is executed.  Then you can inspect current values of variables,
+      and so on.  For example, suppose \file{a.py} contains just this
+      module docstring:
+
+\begin{verbatim}
+"""
+>>> def f(x):
+...     g(x*2)
+>>> def g(x):
+...     print x+3
+...     import pdb; pdb.set_trace()
+>>> f(3)
+9
+"""
+\end{verbatim}
+
+      Then an interactive Python session may look like this:
+
+\begin{verbatim}
+>>> import a, doctest
+>>> doctest.testmod(a)
+--Return--
+> <doctest a[1]>(3)g()->None
+-> import pdb; pdb.set_trace()
+(Pdb) list
+  1     def g(x):
+  2         print x+3
+  3  ->     import pdb; pdb.set_trace()
+[EOF]
+(Pdb) print x
+6
+(Pdb) step
+--Return--
+> <doctest a[0]>(2)f()->None
+-> g(x*2)
+(Pdb) list
+  1     def f(x):
+  2  ->     g(x*2)
+[EOF]
+(Pdb) print x
+3
+(Pdb) step
+--Return--
+> <doctest a[2]>(1)?()->None
+-> f(3)
+(Pdb) cont
+(0, 3)
+>>>
+\end{verbatim}
+
+    \versionchanged[The ability to use \code{pdb.set_trace()} usefully
+                    inside doctests was added]{2.4}
+\end{itemize}
+
+Functions that convert doctests to Python code, and possibly run
+the synthesized code under the debugger:
+
+\begin{funcdesc}{script_from_examples}{s}
+  Convert text with examples to a script.
+
+  Argument \var{s} is a string containing doctest examples.  The string
+  is converted to a Python script, where doctest examples in \var{s}
+  are converted to regular code, and everything else is converted to
+  Python comments.  The generated script is returned as a string.
+  For example, given file \file{a.py} as above,
+
+    \begin{verbatim}
+    >>> print doctest.script_from_examples(open("a.py").read())
+    # """
+    def f(x):
+        g(x*2)
+    def g(x):
+        print x+3
+        import pdb; pdb.set_trace()
+    f(3)
+    # Expected:
+    ## 9
+    ## """
+    \end{verbatim}
+
+  \versionadded{2.4}
+\end{funcdesc}
+
+\begin{funcdesc}{testsource}{module, name}
+   Convert the doctest for an object to a script.
+
+   Argument \var{module} is a module object, or dotted name of a module,
+   containing the object whose doctests are of interest.  Argument
+   \var{name} is the name (within the module) of the object with the
+   doctests of interest.  The result is a string, containing the
+   object's docstring converted to a Python script, as described for
+   \function{script_from_examples()} above.  For example, if module
+   \file{a.py} contains a top-level function \function{f()}, then
 
-\begin{funcdesc}{debug}{module, name}
-  Debug a single doctest docstring.
+    \begin{verbatim}
+    import a, doctest
+    print doctest.testsource(a, "a.f")
+    \end{verbatim}
 
-  Provide the \var{module} (or dotted name of the module) containing
-  the docstring to be debugged and the fully qualified dotted
-  \var{name} of the object with the docstring to be debugged.
+  prints a script version of function \function{f()}'s docstring,
+  with doctests converted to code, and the rest placed in comments.
 
-  The doctest examples are extracted (see function \function{testsource()}),
-  and written to a temporary file.  The Python debugger, \refmodule{pdb},
-  is then invoked on that file.
   \versionadded{2.3}
 \end{funcdesc}
 
+\begin{funcdesc}{debug}{module, name\optional{, pm}}
+  Debug the doctests for an object.
+
+  The \var{module} and \var{name} arguments are the same as for function
+  \function{testsource()} above.  The synthesized Python script for the
+  named object's docstring is written to a temporary file, and then that
+  file is run under the control of the Python debugger, \refmodule{pdb}.
+
+  A shallow copy of \code{\var{module}.__dict__} is used for both local
+  and global execution context.
+
+  Optional argument \var{pm} controls whether post-mortem debugging is
+  used.  If \var{pm} has a true value, the script file is run directly,
+  and the debugger gets involved only if the script terminates via raising
+  an unhandled exception.  If it does, then post-mortem debugging is
+  invoked, via \code{pdb.post_mortem()}, passing the traceback object
+  from the unhandled exception.  If \var{pm} is not specified, or is false,
+  the script is run under the debugger from the start, via passing an
+  appropriate \function{execfile()} call to \code{pdb.run()}.
+
+  \versionadded{2.3}
+
+  \versionchanged[The \var{pm} argument was added]{2.4}
+\end{funcdesc}
+
+\begin{funcdesc}{debug_src}{src\optional{, pm}\optional{, globs}}
+  Debug the doctests in a string.
+
+  This is like function \function{debug()} above, except that
+  a string containing doctest examples is specified directly, via
+  the \var{src} argument.
+
+  Optional argument \var{pm} has the same meaning as in function
+  \function{debug()} above.
+
+  Optional argument \var{globs} gives a dictionary to use as both
+  local and global execution context.  If not specified, or \code{None},
+  an empty dictionary is used.  If specified, a shallow copy of the
+  dictionary is used.
+
+  \versionadded{2.4}
+\end{funcdesc}
+
+The \class{DebugRunner} class, and the special exceptions it may raise,
+are of most interest to testing framework authors, and will only be
+sketched here.  See the source code, and especially \class{DebugRunner}'s
+docstring (which is a doctest!) for more details:
+
 \begin{classdesc}{DebugRunner}{\optional{checker}\optional{,
                                  verbose}\optional{, optionflags}}
 
@@ -1591,6 +1731,9 @@ Doctest provides three mechanisms for debugging doctest examples:
     section~\ref{doctest-advanced-api}.
 \end{classdesc}
 
+There are two exceptions that may be raised by \class{DebugRunner}
+instances:
+
 \begin{excclassdesc}{DocTestFailure}{test, example, got}
     An exception thrown by \class{DocTestRunner} to signal that a
     doctest example's actual output did not match its expected output.
@@ -1608,20 +1751,7 @@ Doctest provides three mechanisms for debugging doctest examples:
     The example's actual output.
 \end{memberdesc}
 
-\begin{funcdesc}{testsource}{module, name}
-  Extract the doctest examples from a docstring.
-
-  Provide the \var{module} (or dotted name of the module) containing the
-  tests to be extracted and the \var{name} (within the module) of the object
-  with the docstring containing the tests to be extracted.
-
-  The doctest examples are returned as a string containing Python
-  code.  The expected output blocks in the examples are converted
-  to Python comments.
-  \versionadded{2.3}
-\end{funcdesc}
-
-\begin{excclassdesc}{UnexpectedException}{test, example, got}
+\begin{excclassdesc}{UnexpectedException}{test, example, exc_info}
     An exception thrown by \class{DocTestRunner} to signal that a
     doctest example raised an unexpected exception.  The constructor
     arguments are used to initialize the member variables of the same