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Oct 27, 2023
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gh-111388: Add show_group to traceback.format_exception_only #111390

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a3155cf
gh-111388: Add `show_group` to `traceback.format_exception_only`
sobolevn Oct 27, 2023
a91e258
It is `:exc:`, not `:exception:`
sobolevn Oct 27, 2023
6f97142
More tests
sobolevn Oct 27, 2023
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9 changes: 8 additions & 1 deletion Doc/library/traceback.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -135,7 +135,7 @@ The module defines the following functions:
text line is not ``None``.


.. function:: format_exception_only(exc, /[, value])
.. function:: format_exception_only(exc, /[, value], *, show_group=False)

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
Expand All @@ -149,13 +149,20 @@ The module defines the following functions:
can be passed as the first argument. If *value* is provided, the first
argument is ignored in order to provide backwards compatibility.

When *show_group* is ``True``, and the exception is an instance of
:exc:`BaseExceptionGroup`, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.

.. versionchanged:: 3.10
The *etype* parameter has been renamed to *exc* and is now
positional-only.

.. versionchanged:: 3.11
The returned list now includes any notes attached to the exception.

.. versionchanged:: 3.13
*show_group* parameter was added.


.. function:: format_exception(exc, /[, value, tb], limit=None, chain=True)

Expand Down
151 changes: 150 additions & 1 deletion Lib/test/test_traceback.py
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Expand Up @@ -215,6 +215,155 @@ def __str__(self):
str_name = '.'.join([X.__module__, X.__qualname__])
self.assertEqual(err[0], "%s: %s\n" % (str_name, str_value))

def test_format_exception_group_without_show_group(self):
eg = ExceptionGroup('A', [ValueError('B')])
err = traceback.format_exception_only(eg)
self.assertEqual(err, ['ExceptionGroup: A (1 sub-exception)\n'])

def test_format_exception_group(self):
eg = ExceptionGroup('A', [ValueError('B')])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (1 sub-exception)\n',
' ValueError: B\n',
])

def test_format_base_exception_group(self):
eg = BaseExceptionGroup('A', [BaseException('B')])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'BaseExceptionGroup: A (1 sub-exception)\n',
' BaseException: B\n',
])

def test_format_exception_group_with_note(self):
exc = ValueError('B')
exc.add_note('Note')
eg = ExceptionGroup('A', [exc])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (1 sub-exception)\n',
' ValueError: B\n',
' Note\n',
])

def test_format_exception_group_explicit_class(self):
eg = ExceptionGroup('A', [ValueError('B')])
err = traceback.format_exception_only(ExceptionGroup, eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (1 sub-exception)\n',
' ValueError: B\n',
])

def test_format_exception_group_multiple_exceptions(self):
eg = ExceptionGroup('A', [ValueError('B'), TypeError('C')])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (2 sub-exceptions)\n',
' ValueError: B\n',
' TypeError: C\n',
])

def test_format_exception_group_multiline_messages(self):
eg = ExceptionGroup('A\n1', [ValueError('B\n2')])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A\n1 (1 sub-exception)\n',
' ValueError: B\n',
' 2\n',
])

def test_format_exception_group_multiline2_messages(self):
exc = ValueError('B\n\n2\n')
exc.add_note('\nC\n\n3')
eg = ExceptionGroup('A\n\n1\n', [exc, IndexError('D')])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A\n\n1\n (2 sub-exceptions)\n',
' ValueError: B\n',
' \n',
' 2\n',
' \n',
' \n', # first char of `note`
' C\n',
' \n',
' 3\n', # note ends
' IndexError: D\n',
])

def test_format_exception_group_syntax_error(self):
exc = SyntaxError("error", ("x.py", 23, None, "bad syntax"))
eg = ExceptionGroup('A\n1', [exc])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A\n1 (1 sub-exception)\n',
' File "x.py", line 23\n',
' bad syntax\n',
' SyntaxError: error\n',
])

def test_format_exception_group_nested_with_notes(self):
exc = IndexError('D')
exc.add_note('Note\nmultiline')
eg = ExceptionGroup('A', [
ValueError('B'),
ExceptionGroup('C', [exc, LookupError('E')]),
TypeError('F'),
])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (3 sub-exceptions)\n',
' ValueError: B\n',
' ExceptionGroup: C (2 sub-exceptions)\n',
' IndexError: D\n',
' Note\n',
' multiline\n',
' LookupError: E\n',
' TypeError: F\n',
])

def test_format_exception_group_with_tracebacks(self):
def f():
try:
1 / 0
except ZeroDivisionError as e:
return e

def g():
try:
raise TypeError('g')
except TypeError as e:
return e

eg = ExceptionGroup('A', [
f(),
ExceptionGroup('B', [g()]),
])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (2 sub-exceptions)\n',
' ZeroDivisionError: division by zero\n',
' ExceptionGroup: B (1 sub-exception)\n',
' TypeError: g\n',
])

def test_format_exception_group_with_cause(self):
def f():
try:
try:
1 / 0
except ZeroDivisionError:
raise ValueError(0)
except Exception as e:
return e

eg = ExceptionGroup('A', [f()])
err = traceback.format_exception_only(eg, show_group=True)
self.assertEqual(err, [
'ExceptionGroup: A (1 sub-exception)\n',
' ValueError: 0\n',
])

@requires_subprocess()
def test_encoded_file(self):
# Test that tracebacks are correctly printed for encoded source files:
Expand Down Expand Up @@ -381,7 +530,7 @@ def test_signatures(self):

self.assertEqual(
str(inspect.signature(traceback.format_exception_only)),
'(exc, /, value=<implicit>)')
'(exc, /, value=<implicit>, *, show_group=False)')


class PurePythonExceptionFormattingMixin:
Expand Down
31 changes: 25 additions & 6 deletions Lib/traceback.py
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Original file line number Diff line number Diff line change
Expand Up @@ -148,7 +148,7 @@ def format_exception(exc, /, value=_sentinel, tb=_sentinel, limit=None, \
return list(te.format(chain=chain))


def format_exception_only(exc, /, value=_sentinel):
def format_exception_only(exc, /, value=_sentinel, *, show_group=False):
"""Format the exception part of a traceback.

The return value is a list of strings, each ending in a newline.
Expand All @@ -158,21 +158,26 @@ def format_exception_only(exc, /, value=_sentinel):
contains several lines that (when printed) display detailed information
about where the syntax error occurred. Following the message, the list
contains the exception's ``__notes__``.

When *show_group* is ``True``, and the exception is an instance of
:exc:`BaseExceptionGroup`, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.
"""
if value is _sentinel:
value = exc
te = TracebackException(type(value), value, None, compact=True)
return list(te.format_exception_only())
return list(te.format_exception_only(show_group=show_group))


# -- not official API but folk probably use these two functions.

def _format_final_exc_line(etype, value):
def _format_final_exc_line(etype, value, *, insert_final_newline=True):
valuestr = _safe_string(value, 'exception')
end_char = "\n" if insert_final_newline else ""
if value is None or not valuestr:
line = "%s\n" % etype
line = f"{etype}{end_char}"
else:
line = "%s: %s\n" % (etype, valuestr)
line = f"{etype}: {valuestr}{end_char}"
return line

def _safe_string(value, what, func=str):
Expand Down Expand Up @@ -889,6 +894,10 @@ def format_exception_only(self, *, show_group=False, _depth=0):
display detailed information about where the syntax error occurred.
Following the message, generator also yields
all the exception's ``__notes__``.

When *show_group* is ``True``, and the exception is an instance of
:exc:`BaseExceptionGroup`, the nested exceptions are included as
well, recursively, with indentation relative to their nesting depth.
"""

indent = 3 * _depth * ' '
Expand All @@ -904,7 +913,17 @@ def format_exception_only(self, *, show_group=False, _depth=0):
stype = smod + '.' + stype

if not issubclass(self.exc_type, SyntaxError):
yield indent + _format_final_exc_line(stype, self._str)
if _depth > 0:
# Nested exceptions needs correct handling of multiline messages.
formatted = _format_final_exc_line(
stype, self._str, insert_final_newline=False,
).split('\n')
yield from [
indent + l + '\n'
for l in formatted
]
else:
yield _format_final_exc_line(stype, self._str)
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Does this fix need to be backported to 3.12/311?

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No, because 3.12 does not have show_group / _depth at all:

cpython/Lib/traceback.py

Lines 865 to 892 in 307ca78

def format_exception_only(self):
"""Format the exception part of the traceback.
The return value is a generator of strings, each ending in a newline.
Generator yields the exception message.
For :exc:`SyntaxError` exceptions, it
also yields (before the exception message)
several lines that (when printed)
display detailed information about where the syntax error occurred.
Following the message, generator also yields
all the exception's ``__notes__``.
"""
if self.exc_type is None:
yield _format_final_exc_line(None, self._str)
return
stype = self.exc_type.__qualname__
smod = self.exc_type.__module__
if smod not in ("__main__", "builtins"):
if not isinstance(smod, str):
smod = "<unknown>"
stype = smod + '.' + stype
if not issubclass(self.exc_type, SyntaxError):
yield _format_final_exc_line(stype, self._str)
else:
yield from self._format_syntax_error(stype)

And without it, the result is identical with and without this fix.

else:
yield from [indent + l for l in self._format_syntax_error(stype)]

Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2023-10-27-09-56-20.gh-issue-111388.SlmDbC.rst
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@@ -0,0 +1,2 @@
Add ``show_group`` parameter to :func:`traceback.format_exception_only`,
which allows to format :exc:`ExceptionGroup` instances.