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+
+:mod:`traceback` --- Print or retrieve a stack traceback
+========================================================
+
+.. module:: traceback
+   :synopsis: Print or retrieve a stack traceback.
+
+
+This module provides a standard interface to extract, format and print stack
+traces of Python programs.  It exactly mimics the behavior of the Python
+interpreter when it prints a stack trace.  This is useful when you want to print
+stack traces under program control, such as in a "wrapper" around the
+interpreter.
+
+.. index:: object: traceback
+
+The module uses traceback objects --- this is the object type that is stored in
+the variables ``sys.exc_traceback`` (deprecated) and ``sys.last_traceback`` and
+returned as the third item from :func:`sys.exc_info`.
+
+The module defines the following functions:
+
+
+.. function:: print_tb(traceback[, limit[, file]])
+
+   Print up to *limit* stack trace entries from *traceback*.  If *limit* is omitted
+   or ``None``, all entries are printed. If *file* is omitted or ``None``, the
+   output goes to ``sys.stderr``; otherwise it should be an open file or file-like
+   object to receive the output.
+
+
+.. function:: print_exception(type, value, traceback[, limit[, file]])
+
+   Print exception information and up to *limit* stack trace entries from
+   *traceback* to *file*. This differs from :func:`print_tb` in the following ways:
+   (1) if *traceback* is not ``None``, it prints a header ``Traceback (most recent
+   call last):``; (2) it prints the exception *type* and *value* after the stack
+   trace; (3) if *type* is :exc:`SyntaxError` and *value* has the appropriate
+   format, it prints the line where the syntax error occurred with a caret
+   indicating the approximate position of the error.
+
+
+.. function:: print_exc([limit[, file]])
+
+   This is a shorthand for ``print_exception(sys.exc_type, sys.exc_value,
+   sys.exc_traceback, limit, file)``.  (In fact, it uses :func:`sys.exc_info` to
+   retrieve the same information in a thread-safe way instead of using the
+   deprecated variables.)
+
+
+.. function:: format_exc([limit])
+
+   This is like ``print_exc(limit)`` but returns a string instead of printing to a
+   file.
+
+   .. versionadded:: 2.4
+
+
+.. function:: print_last([limit[, file]])
+
+   This is a shorthand for ``print_exception(sys.last_type, sys.last_value,
+   sys.last_traceback, limit, file)``.
+
+
+.. function:: print_stack([f[, limit[, file]]])
+
+   This function prints a stack trace from its invocation point.  The optional *f*
+   argument can be used to specify an alternate stack frame to start.  The optional
+   *limit* and *file* arguments have the same meaning as for
+   :func:`print_exception`.
+
+
+.. function:: extract_tb(traceback[, limit])
+
+   Return a list of up to *limit* "pre-processed" stack trace entries extracted
+   from the traceback object *traceback*.  It is useful for alternate formatting of
+   stack traces.  If *limit* is omitted or ``None``, all entries are extracted.  A
+   "pre-processed" stack trace entry is a quadruple (*filename*, *line number*,
+   *function name*, *text*) representing the information that is usually printed
+   for a stack trace.  The *text* is a string with leading and trailing whitespace
+   stripped; if the source is not available it is ``None``.
+
+
+.. function:: extract_stack([f[, limit]])
+
+   Extract the raw traceback from the current stack frame.  The return value has
+   the same format as for :func:`extract_tb`.  The optional *f* and *limit*
+   arguments have the same meaning as for :func:`print_stack`.
+
+
+.. function:: format_list(list)
+
+   Given a list of tuples as returned by :func:`extract_tb` or
+   :func:`extract_stack`, return a list of strings ready for printing.  Each string
+   in the resulting list corresponds to the item with the same index in the
+   argument list.  Each string ends in a newline; the strings may contain internal
+   newlines as well, for those items whose source text line is not ``None``.
+
+
+.. function:: format_exception_only(type, value)
+
+   Format the exception part of a traceback.  The arguments are the exception type
+   and value such as given by ``sys.last_type`` and ``sys.last_value``.  The return
+   value is a list of strings, each ending in a newline.  Normally, the list
+   contains a single string; however, for :exc:`SyntaxError` exceptions, it
+   contains several lines that (when printed) display detailed information about
+   where the syntax error occurred.  The message indicating which exception
+   occurred is the always last string in the list.
+
+
+.. function:: format_exception(type, value, tb[, limit])
+
+   Format a stack trace and the exception information.  The arguments  have the
+   same meaning as the corresponding arguments to :func:`print_exception`.  The
+   return value is a list of strings, each ending in a newline and some containing
+   internal newlines.  When these lines are concatenated and printed, exactly the
+   same text is printed as does :func:`print_exception`.
+
+
+.. function:: format_tb(tb[, limit])
+
+   A shorthand for ``format_list(extract_tb(tb, limit))``.
+
+
+.. function:: format_stack([f[, limit]])
+
+   A shorthand for ``format_list(extract_stack(f, limit))``.
+
+
+.. function:: tb_lineno(tb)
+
+   This function returns the current line number set in the traceback object.  This
+   function was necessary because in versions of Python prior to 2.3 when the
+   :option:`-O` flag was passed to Python the ``tb.tb_lineno`` was not updated
+   correctly.  This function has no use in versions past 2.3.
+
+
+.. _traceback-example:
+
+Traceback Example
+-----------------
+
+This simple example implements a basic read-eval-print loop, similar to (but
+less useful than) the standard Python interactive interpreter loop.  For a more
+complete implementation of the interpreter loop, refer to the :mod:`code`
+module. ::
+
+   import sys, traceback
+
+   def run_user_code(envdir):
+       source = raw_input(">>> ")
+       try:
+           exec source in envdir
+       except:
+           print "Exception in user code:"
+           print '-'*60
+           traceback.print_exc(file=sys.stdout)
+           print '-'*60
+
+   envdir = {}
+   while 1:
+       run_user_code(envdir)
+