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YvesDup opened this issue Apr 9, 2025 · 2 comments
Open

TracebackException swallows attributes of falsey Exception and falsey ExceptionGroup. #132308

YvesDup opened this issue Apr 9, 2025 · 2 comments
Labels
stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@YvesDup
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YvesDup commented Apr 9, 2025 •
edited by bedevere-app bot
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Bug report

Bug description:

Description

import traceback as tb

class FalseyLenException(Exception):
    def __len__(self):
        return 0

class FalseyBoolException(Exception):
    def __bool__(self):
        return False

def tracebackexception_swallows_cause_and_context():
    try:
        raise FalseyBoolException("Oh") from KeyError
    except Exception as e:
        print(f'{e = }, {e.__cause__ = }')
        tb.print_exception(e)
    print("---"*20)

    try:
        try:
            1/0
        except:
            raise FalseyLenException("Ah")
    except Exception as e:
        print(f'{e = }, {e.__context__ = }')
        tb.print_exception(e)
    print("---"*20)

if __name__ == "__main__":
    tracebackexception_swallows_cause_and_context()

Ouptput is:

e = FalseyBoolException('Oh'), e.__cause__ = KeyError()
Traceback (most recent call last):
  File "/Users/yves/Desktop/Bugs/gh-132XXX.py", line 13, in tracebackexception_swallows_cause_and_context
    raise FalseyBoolException("Oh") from KeyError
FalseyBoolException: Oh
------------------------------------------------------------
e = FalseyLenException('Ah'), e.__context__ = ZeroDivisionError('division by zero')
Traceback (most recent call last):
  File "/Users/yves/Desktop/Bugs/gh-132XXX.py", line 23, in tracebackexception_swallows_cause_and_context
    raise FalseyLenException("Ah")
FalseyLenException: Ah

The Cause or Context descriptions are not printed as expected.

Where Does it from ?

These following tests are wrong.

cpython/Lib/traceback.py

Line 1123 in 255eb37

if (e and e.__cause__ is not None

It should be: if (e is not None and e.__cause__ is not None

cpython/Lib/traceback.py

Line 1144 in 255eb37

if (e and e.__context__ is not None

It should be: if (e is not None and and e.__context__ is not None

Linked Issues

See: #132129

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs
@YvesDup YvesDup added the type-bug An unexpected behavior, bug, or error label Apr 9, 2025
@ZeroIntensity ZeroIntensity added the stdlib Python modules in the Lib dir label Apr 9, 2025
@YvesDup
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YvesDup commented Apr 9, 2025 •
edited
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TracebackException class also swallows sub-exceptions of falsey exception group.

def tracebackexception_swallows_exceptiongroup():
    # Works fine.
    try:
        raise ExceptionGroup("Gah", (KeyError('1'), NameError('Goh')))
    except Exception as e:
        print(f'{e = }, {e.__cause__ = }')
        tb.print_exception(e)
    print("---"*20)

    # Swallows details.
    try:
        raise FalseyExceptionGroup("Gih", (KeyError(2), NameError('Guh')))
    except Exception as ee:
        print(f'{ee = }, {ee.__cause__ = }')
        tb.print_exception(ee)
    print("---"*20)

if __name__ == "__main__":
    tracebackexception_swallows_exceptiongroup()

Output is:

e = ExceptionGroup('Gah', (KeyError('1'), NameError('Goh'))), e.__cause__ = None
  + Exception Group Traceback (most recent call last):
  |   File "/Users/yves/Desktop/Bugs/gh-132308.py", line 37, in tracebackexception_swallows_exceptiongroup
  |     raise ExceptionGroup("Gah", (KeyError('1'), NameError('Goh')))
  | ExceptionGroup: Gah (2 sub-exceptions)
  +-+---------------- 1 ----------------
    | KeyError: '1'
    +---------------- 2 ----------------
    | NameError: Goh
    +------------------------------------
------------------------------------------------------------
ee = FalseyExceptionGroup('Gih', (KeyError(2), NameError('Guh'))), ee.__cause__ = None
Traceback (most recent call last):
  File "/Users/yves/Desktop/Bugs/gh-132308.py", line 45, in tracebackexception_swallows_exceptiongroup
    raise FalseyExceptionGroup("Gih", (KeyError(2), NameError('Guh')))
FalseyExceptionGroup: Gih (2 sub-exceptions)
------------------------------------------------------------

As below, a wrong test must be change.

cpython/Lib/traceback.py

Line 1159 in 255eb37

if e and isinstance(e, BaseExceptionGroup):

@YvesDup YvesDup changed the title TracebackException swallows __cause__ and __context__ attributes of falsey exceptions. TracebackException swallows attributes of falsey Exception and falsey ExceptionGroup. Apr 9, 2025
@iritkatriel
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Thank you. Would you like to make a PR?

@bedevere-app bedevere-app bot mentioned this issue Apr 10, 2025
Merged
picnixz pushed a commit that referenced this issue Apr 19, 2025
@YvesDup
gh-132308: prevent TracebackException swallowing attributes of a fa…
69cda31 
…lsey `Exception` or `ExceptionGroup` (#132363)
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Apr 19, 2025
@YvesDup @miss-islington
pythongh-132308: prevent TracebackException swallowing attributes o…
c36f07d 
…f a falsey `Exception` or `ExceptionGroup` (pythonGH-132363)

(cherry picked from commit 69cda31)

Co-authored-by: Duprat <yduprat@gmail.com>
@bedevere-app bedevere-app bot mentioned this issue Apr 19, 2025
Merged
picnixz pushed a commit that referenced this issue Apr 30, 2025
@miss-islington @YvesDup
[3.13] gh-132308: prevent TracebackException swallowing attributes …
dfaa384 
…of a falsey `Exception` or `ExceptionGroup` (GH-132363) (#132725)

gh-132308: prevent `TracebackException` swallowing attributes of a falsey `Exception` or `ExceptionGroup` (GH-132363)
(cherry picked from commit 69cda31)

Co-authored-by: Duprat <yduprat@gmail.com>
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