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

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TracebackException swallows attributes of falsey Exception and falsey ExceptionGroup.#132308
Labels
stdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@YvesDup
YvesDup
opened on Apr 9, 2025

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

Activity

  1. YvesDup
    added
    type-bugAn unexpected behavior, bug, or error
    on Apr 9, 2025
  2. ZeroIntensity
    added
    stdlibStandard Library Python modules in the Lib/ directory
    on Apr 9, 2025

  3. YvesDup commented on Apr 9, 2025

    @YvesDup
    YvesDup
    on Apr 9, 2025
    ContributorAuthor

    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):

  4. YvesDup
    changed the title [-]`TracebackException` swallows `__cause__` and `__context__` attributes of falsey exceptions.[/-] [+]`TracebackException` swallows attributes of falsey Exception and falsey ExceptionGroup.[/+] on Apr 9, 2025

  5. iritkatriel commented on Apr 9, 2025

    @iritkatriel
    iritkatriel
    on Apr 9, 2025
    Member

    Thank you. Would you like to make a PR?

  6. picnixz
    added a commit that references this issue on Apr 19, 2025

    gh-132308: prevent `TracebackException` swallowing attributes of a fa…

    69cda31
  7. miss-islington
    added a commit that references this issue on Apr 19, 2025

    pythongh-132308: prevent `TracebackException` swallowing attributes o…

    c36f07d
  8. picnixz
    added a commit that references this issue on Apr 30, 2025

    [3.13] gh-132308: prevent `TracebackException` swallowing attributes …

    dfaa384
  9. YvesDup
    closed this as completedon Jul 30, 2025
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