From 91e93794d5dd1aa91fbe142099c2955e0c4c1660 Mon Sep 17 00:00:00 2001 From: Zackery Spytz Date: Thu, 5 Nov 2020 15:18:44 -0700 Subject: bpo-26389: Allow passing an exception object in the traceback module (GH-22610) The format_exception(), format_exception_only(), and print_exception() functions can now take an exception object as a positional-only argument. Co-Authored-By: Matthias Bussonnier --- Doc/library/traceback.rst | 43 ++++++++++++++++------ Doc/whatsnew/3.10.rst | 18 +++++++++ Lib/test/test_traceback.py | 20 ++++++++++ Lib/traceback.py | 36 +++++++++++------- .../2020-10-08-23-51-55.bpo-26389.uga44e.rst | 4 ++ 5 files changed, 97 insertions(+), 24 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2020-10-08-23-51-55.bpo-26389.uga44e.rst diff --git a/Doc/library/traceback.rst b/Doc/library/traceback.rst index 462a6a5..c233f18 100644 --- a/Doc/library/traceback.rst +++ b/Doc/library/traceback.rst @@ -36,7 +36,8 @@ The module defines the following functions: Added negative *limit* support. -.. function:: print_exception(etype, value, tb, limit=None, file=None, chain=True) +.. function:: print_exception(exc, /[, value, tb], limit=None, \ + file=None, chain=True) Print exception information and stack trace entries from traceback object *tb* to *file*. This differs from :func:`print_tb` in the following @@ -45,7 +46,7 @@ The module defines the following functions: * if *tb* is not ``None``, it prints a header ``Traceback (most recent call last):`` - * it prints the exception *etype* and *value* after the stack trace + * it prints the exception type and *value* after the stack trace .. index:: single: ^ (caret); marker @@ -53,6 +54,10 @@ The module defines the following functions: format, it prints the line where the syntax error occurred with a caret indicating the approximate position of the error. + Since Python 3.10, instead of passing *value* and *tb*, an exception object + can be passed as the first argument. If *value* and *tb* are provided, the + first argument is ignored in order to provide backwards compatibility. + The optional *limit* argument has the same meaning as for :func:`print_tb`. If *chain* is true (the default), then chained exceptions (the :attr:`__cause__` or :attr:`__context__` attributes of the exception) will be @@ -62,6 +67,10 @@ The module defines the following functions: .. versionchanged:: 3.5 The *etype* argument is ignored and inferred from the type of *value*. + .. versionchanged:: 3.10 + The *etype* parameter has been renamed to *exc* and is now + positional-only. + .. function:: print_exc(limit=None, file=None, chain=True) @@ -121,18 +130,26 @@ The module defines the following functions: text line is not ``None``. -.. function:: format_exception_only(etype, value) +.. function:: format_exception_only(exc, /[, value]) + + Format the exception part of a traceback using an exception value such as + given by ``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. - 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. + Since Python 3.10, instead of passing *value*, an exception object + can be passed as the first argument. If *value* is provided, the first + argument is ignored in order to provide backwards compatibility. + .. versionchanged:: 3.10 + The *etype* parameter has been renamed to *exc* and is now + positional-only. -.. function:: format_exception(etype, value, tb, limit=None, chain=True) + +.. function:: format_exception(exc, /[, value, tb], limit=None, chain=True) Format a stack trace and the exception information. The arguments have the same meaning as the corresponding arguments to :func:`print_exception`. The @@ -143,6 +160,10 @@ The module defines the following functions: .. versionchanged:: 3.5 The *etype* argument is ignored and inferred from the type of *value*. + .. versionchanged:: 3.10 + This function's behavior and signature were modified to match + :func:`print_exception`. + .. function:: format_exc(limit=None, chain=True) diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst index bac1a2e..0ed7084 100644 --- a/Doc/whatsnew/3.10.rst +++ b/Doc/whatsnew/3.10.rst @@ -232,6 +232,15 @@ retrieve the functions set by :func:`threading.settrace` and :func:`threading.setprofile` respectively. (Contributed by Mario Corchero in :issue:`42251`.) +traceback +--------- + +The :func:`~traceback.format_exception`, +:func:`~traceback.format_exception_only`, and +:func:`~traceback.print_exception` functions can now take an exception object +as a positional-only argument. +(Contributed by Zackery Spytz and Matthias Bussonnier in :issue:`26389`.) + types ----- @@ -328,6 +337,15 @@ This section lists previously described changes and other bugfixes that may require changes to your code. +Changes in the Python API +------------------------- + +* The *etype* parameters of the :func:`~traceback.format_exception`, + :func:`~traceback.format_exception_only`, and + :func:`~traceback.print_exception` functions in the :mod:`traceback` module + have been renamed to *exc*. + (Contributed by Zackery Spytz and Matthias Bussonnier in :issue:`26389`.) + Build Changes ============= diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py index 730596e..91688ff 100644 --- a/Lib/test/test_traceback.py +++ b/Lib/test/test_traceback.py @@ -212,6 +212,26 @@ class TracebackCases(unittest.TestCase): ) self.assertEqual(output.getvalue(), "Exception: projector\n") + def test_print_exception_exc(self): + output = StringIO() + traceback.print_exception(Exception("projector"), file=output) + self.assertEqual(output.getvalue(), "Exception: projector\n") + + def test_format_exception_exc(self): + e = Exception("projector") + output = traceback.format_exception(e) + self.assertEqual(output, ["Exception: projector\n"]) + with self.assertRaisesRegex(ValueError, 'Both or neither'): + traceback.format_exception(e.__class__, e) + with self.assertRaisesRegex(ValueError, 'Both or neither'): + traceback.format_exception(e.__class__, tb=e.__traceback__) + with self.assertRaisesRegex(TypeError, 'positional-only'): + traceback.format_exception(exc=e) + + def test_format_exception_only_exc(self): + output = traceback.format_exception_only(Exception("projector")) + self.assertEqual(output, ["Exception: projector\n"]) + class TracebackFormatTests(unittest.TestCase): diff --git a/Lib/traceback.py b/Lib/traceback.py index a19e387..d2d93c8 100644 --- a/Lib/traceback.py +++ b/Lib/traceback.py @@ -84,7 +84,19 @@ _context_message = ( "another exception occurred:\n\n") -def print_exception(etype, value, tb, limit=None, file=None, chain=True): +_sentinel = object() + + +def _parse_value_tb(exc, value, tb): + if (value is _sentinel) != (tb is _sentinel): + raise ValueError("Both or neither of value and tb must be given") + if value is tb is _sentinel: + return exc, exc.__traceback__ + return value, tb + + +def print_exception(exc, /, value=_sentinel, tb=_sentinel, limit=None, \ + file=None, chain=True): """Print exception up to 'limit' stack trace entries from 'tb' to 'file'. This differs from print_tb() in the following ways: (1) if @@ -95,9 +107,7 @@ def print_exception(etype, value, tb, limit=None, file=None, chain=True): occurred with a caret on the next line indicating the approximate position of the error. """ - # format_exception has ignored etype for some time, and code such as cgitb - # passes in bogus values as a result. For compatibility with such code we - # ignore it here (rather than in the new TracebackException API). + value, tb = _parse_value_tb(exc, value, tb) if file is None: file = sys.stderr for line in TracebackException( @@ -105,7 +115,8 @@ def print_exception(etype, value, tb, limit=None, file=None, chain=True): print(line, file=file, end="") -def format_exception(etype, value, tb, limit=None, chain=True): +def format_exception(exc, /, value=_sentinel, tb=_sentinel, limit=None, \ + chain=True): """Format a stack trace and the exception information. The arguments have the same meaning as the corresponding arguments @@ -114,19 +125,15 @@ def format_exception(etype, value, tb, limit=None, chain=True): these lines are concatenated and printed, exactly the same text is printed as does print_exception(). """ - # format_exception has ignored etype for some time, and code such as cgitb - # passes in bogus values as a result. For compatibility with such code we - # ignore it here (rather than in the new TracebackException API). + value, tb = _parse_value_tb(exc, value, tb) return list(TracebackException( type(value), value, tb, limit=limit).format(chain=chain)) -def format_exception_only(etype, value): +def format_exception_only(exc, /, value=_sentinel): """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. + The return value is a list of strings, each ending in a newline. Normally, the list contains a single string; however, for SyntaxError exceptions, it contains several lines that (when @@ -137,7 +144,10 @@ def format_exception_only(etype, value): string in the list. """ - return list(TracebackException(etype, value, None).format_exception_only()) + if value is _sentinel: + value = exc + return list(TracebackException( + type(value), value, None).format_exception_only()) # -- not official API but folk probably use these two functions. diff --git a/Misc/NEWS.d/next/Library/2020-10-08-23-51-55.bpo-26389.uga44e.rst b/Misc/NEWS.d/next/Library/2020-10-08-23-51-55.bpo-26389.uga44e.rst new file mode 100644 index 0000000..a721a0d --- /dev/null +++ b/Misc/NEWS.d/next/Library/2020-10-08-23-51-55.bpo-26389.uga44e.rst @@ -0,0 +1,4 @@ +The :func:`traceback.format_exception`, +:func:`traceback.format_exception_only`, and +:func:`traceback.print_exception` functions can now take an exception object +as a positional-only argument. -- cgit v0.12