2007-08-15 11:28:01 -03:00
|
|
|
: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
|
2009-04-27 14:22:36 -03:00
|
|
|
the variables :data:`sys.exc_traceback` (deprecated) and :data:`sys.last_traceback` and
|
2007-08-15 11:28:01 -03:00
|
|
|
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,
|
2009-04-27 14:22:36 -03:00
|
|
|
sys.last_traceback, limit, file)``. In general it will work only after
|
|
|
|
an exception has reached an interactive prompt (see :data:`sys.last_type`).
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
|
|
|
|
.. 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
|
2014-04-02 02:11:34 -03:00
|
|
|
"pre-processed" stack trace entry is a 4-tuple (*filename*, *line number*,
|
2007-08-15 11:28:01 -03:00
|
|
|
*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:
|
|
|
|
|
2007-12-05 13:56:50 -04:00
|
|
|
Traceback Examples
|
|
|
|
------------------
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
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. ::
|
|
|
|
|
2009-02-19 23:31:23 -04:00
|
|
|
import sys, traceback
|
2007-08-15 11:28:01 -03:00
|
|
|
|
|
|
|
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)
|
|
|
|
|
2007-12-05 13:56:50 -04:00
|
|
|
|
|
|
|
The following example demonstrates the different ways to print and format the
|
|
|
|
exception and traceback::
|
|
|
|
|
2009-02-19 23:31:23 -04:00
|
|
|
import sys, traceback
|
2007-12-05 13:56:50 -04:00
|
|
|
|
|
|
|
def lumberjack():
|
|
|
|
bright_side_of_death()
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2007-12-05 13:56:50 -04:00
|
|
|
def bright_side_of_death():
|
|
|
|
return tuple()[0]
|
2009-01-03 16:55:06 -04:00
|
|
|
|
2007-12-05 13:56:50 -04:00
|
|
|
try:
|
|
|
|
lumberjack()
|
2010-03-12 21:21:34 -04:00
|
|
|
except IndexError:
|
|
|
|
exc_type, exc_value, exc_traceback = sys.exc_info()
|
2007-12-05 13:56:50 -04:00
|
|
|
print "*** print_tb:"
|
2010-03-12 21:21:34 -04:00
|
|
|
traceback.print_tb(exc_traceback, limit=1, file=sys.stdout)
|
2007-12-05 13:56:50 -04:00
|
|
|
print "*** print_exception:"
|
2010-03-12 21:21:34 -04:00
|
|
|
traceback.print_exception(exc_type, exc_value, exc_traceback,
|
2007-12-05 13:56:50 -04:00
|
|
|
limit=2, file=sys.stdout)
|
|
|
|
print "*** print_exc:"
|
|
|
|
traceback.print_exc()
|
|
|
|
print "*** format_exc, first and last line:"
|
|
|
|
formatted_lines = traceback.format_exc().splitlines()
|
|
|
|
print formatted_lines[0]
|
|
|
|
print formatted_lines[-1]
|
|
|
|
print "*** format_exception:"
|
2010-03-12 21:21:34 -04:00
|
|
|
print repr(traceback.format_exception(exc_type, exc_value,
|
|
|
|
exc_traceback))
|
2007-12-05 13:56:50 -04:00
|
|
|
print "*** extract_tb:"
|
2010-03-12 21:21:34 -04:00
|
|
|
print repr(traceback.extract_tb(exc_traceback))
|
2007-12-05 13:56:50 -04:00
|
|
|
print "*** format_tb:"
|
2010-03-12 21:21:34 -04:00
|
|
|
print repr(traceback.format_tb(exc_traceback))
|
|
|
|
print "*** tb_lineno:", exc_traceback.tb_lineno
|
2007-12-05 13:56:50 -04:00
|
|
|
|
|
|
|
|
|
|
|
The output for the example would look similar to this::
|
|
|
|
|
|
|
|
*** print_tb:
|
2009-04-27 14:22:36 -03:00
|
|
|
File "<doctest...>", line 10, in <module>
|
2007-12-05 13:56:50 -04:00
|
|
|
lumberjack()
|
|
|
|
*** print_exception:
|
|
|
|
Traceback (most recent call last):
|
2009-04-27 14:22:36 -03:00
|
|
|
File "<doctest...>", line 10, in <module>
|
2007-12-05 13:56:50 -04:00
|
|
|
lumberjack()
|
2009-04-27 14:22:36 -03:00
|
|
|
File "<doctest...>", line 4, in lumberjack
|
2007-12-05 13:56:50 -04:00
|
|
|
bright_side_of_death()
|
|
|
|
IndexError: tuple index out of range
|
|
|
|
*** print_exc:
|
|
|
|
Traceback (most recent call last):
|
2009-04-27 14:22:36 -03:00
|
|
|
File "<doctest...>", line 10, in <module>
|
2007-12-05 13:56:50 -04:00
|
|
|
lumberjack()
|
2009-04-27 14:22:36 -03:00
|
|
|
File "<doctest...>", line 4, in lumberjack
|
2007-12-05 13:56:50 -04:00
|
|
|
bright_side_of_death()
|
|
|
|
IndexError: tuple index out of range
|
|
|
|
*** format_exc, first and last line:
|
|
|
|
Traceback (most recent call last):
|
|
|
|
IndexError: tuple index out of range
|
|
|
|
*** format_exception:
|
|
|
|
['Traceback (most recent call last):\n',
|
2009-04-27 14:22:36 -03:00
|
|
|
' File "<doctest...>", line 10, in <module>\n lumberjack()\n',
|
|
|
|
' File "<doctest...>", line 4, in lumberjack\n bright_side_of_death()\n',
|
|
|
|
' File "<doctest...>", line 7, in bright_side_of_death\n return tuple()[0]\n',
|
2007-12-05 13:56:50 -04:00
|
|
|
'IndexError: tuple index out of range\n']
|
|
|
|
*** extract_tb:
|
2009-04-27 14:22:36 -03:00
|
|
|
[('<doctest...>', 10, '<module>', 'lumberjack()'),
|
|
|
|
('<doctest...>', 4, 'lumberjack', 'bright_side_of_death()'),
|
2009-04-28 16:02:55 -03:00
|
|
|
('<doctest...>', 7, 'bright_side_of_death', 'return tuple()[0]')]
|
2007-12-05 13:56:50 -04:00
|
|
|
*** format_tb:
|
2009-04-27 14:22:36 -03:00
|
|
|
[' File "<doctest...>", line 10, in <module>\n lumberjack()\n',
|
|
|
|
' File "<doctest...>", line 4, in lumberjack\n bright_side_of_death()\n',
|
|
|
|
' File "<doctest...>", line 7, in bright_side_of_death\n return tuple()[0]\n']
|
|
|
|
*** tb_lineno: 10
|
2007-12-05 13:56:50 -04:00
|
|
|
|
2009-04-28 16:02:55 -03:00
|
|
|
|
2007-12-05 13:56:50 -04:00
|
|
|
The following example shows the different ways to print and format the stack::
|
|
|
|
|
|
|
|
>>> import traceback
|
|
|
|
>>> def another_function():
|
|
|
|
... lumberstack()
|
2009-01-03 16:55:06 -04:00
|
|
|
...
|
2007-12-05 13:56:50 -04:00
|
|
|
>>> def lumberstack():
|
|
|
|
... traceback.print_stack()
|
|
|
|
... print repr(traceback.extract_stack())
|
|
|
|
... print repr(traceback.format_stack())
|
2009-01-03 16:55:06 -04:00
|
|
|
...
|
2007-12-05 13:56:50 -04:00
|
|
|
>>> another_function()
|
|
|
|
File "<doctest>", line 10, in <module>
|
|
|
|
another_function()
|
|
|
|
File "<doctest>", line 3, in another_function
|
|
|
|
lumberstack()
|
|
|
|
File "<doctest>", line 6, in lumberstack
|
|
|
|
traceback.print_stack()
|
|
|
|
[('<doctest>', 10, '<module>', 'another_function()'),
|
|
|
|
('<doctest>', 3, 'another_function', 'lumberstack()'),
|
|
|
|
('<doctest>', 7, 'lumberstack', 'print repr(traceback.extract_stack())')]
|
|
|
|
[' File "<doctest>", line 10, in <module>\n another_function()\n',
|
|
|
|
' File "<doctest>", line 3, in another_function\n lumberstack()\n',
|
|
|
|
' File "<doctest>", line 8, in lumberstack\n print repr(traceback.format_stack())\n']
|
|
|
|
|
|
|
|
|
2009-04-27 14:22:36 -03:00
|
|
|
This last example demonstrates the final few formatting functions:
|
|
|
|
|
|
|
|
.. doctest::
|
|
|
|
:options: +NORMALIZE_WHITESPACE
|
2007-12-05 13:56:50 -04:00
|
|
|
|
|
|
|
>>> import traceback
|
2009-04-27 12:09:25 -03:00
|
|
|
>>> traceback.format_list([('spam.py', 3, '<module>', 'spam.eggs()'),
|
|
|
|
... ('eggs.py', 42, 'eggs', 'return "bacon"')])
|
2007-12-05 13:56:50 -04:00
|
|
|
[' File "spam.py", line 3, in <module>\n spam.eggs()\n',
|
|
|
|
' File "eggs.py", line 42, in eggs\n return "bacon"\n']
|
2009-04-27 12:09:25 -03:00
|
|
|
>>> an_error = IndexError('tuple index out of range')
|
|
|
|
>>> traceback.format_exception_only(type(an_error), an_error)
|
2007-12-05 13:56:50 -04:00
|
|
|
['IndexError: tuple index out of range\n']
|