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asyncio.Timeout.__aexit__ does not handle BaseExceptionGroup #137549

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asyncio.Timeout.__aexit__ does not handle BaseExceptionGroup#137549
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corona10gunyu1019
Labels
stdlibStandard Library Python modules in the Lib/ directorytopic-asynciotype-bugAn unexpected behavior, bug, or error

Description

@PLPeeters
PLPeeters
opened on Aug 8, 2025

Bug report

Bug description:

There may be a good reason for this I am not seeing, but in the asyncio.Timeout.__aexit__ handler, the exception group handling seems too narrow:

cpython/Lib/asyncio/timeouts.py

Lines 113 to 119 in 9743d06

if issubclass(exc_type, exceptions.CancelledError):
raise TimeoutError from exc_val
elif exc_val is not None:
self._insert_timeout_error(exc_val)
if isinstance(exc_val, ExceptionGroup):
for exc in exc_val.exceptions:
self._insert_timeout_error(exc)

Given exc_val itself can be a BaseException and _insert_timeout_error takes a BaseException as an argument, I fail to see a reason not to check for superclass BaseExceptionGroup instead.

cpython/Lib/asyncio/timeouts.py

Line 133 in 9743d06

def _insert_timeout_error(exc_val: BaseException) -> None:

This no longer impacts me as I implemented what I was aiming for in a better way, but it still looks like a bug. Is it?

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

Activity

  1. PLPeeters
    added
    type-bugAn unexpected behavior, bug, or error
    on Aug 8, 2025
  2. picnixz
    added
    topic-asyncio
    stdlibStandard Library Python modules in the Lib/ directory
    on Aug 8, 2025
  3. github-project-automation
    added this to asyncioon Aug 8, 2025
  4. github-project-automation
    moved this to Todo in asyncioon Aug 8, 2025

  5. gunyu1019 commented on Aug 15, 2025

    @gunyu1019
    gunyu1019
    on Aug 15, 2025

    @corona10, Let me try to fix this issue.

  6. corona10
    self-assigned this
    on Aug 15, 2025

  7. corona10 commented on Aug 15, 2025

    @corona10
    corona10
    on Aug 15, 2025
    Member

    Please go ahead!

  8. corona10
    assigned
    gunyu1019
    on Aug 15, 2025
  9. eunbie07
    added a commit that references this issue on Aug 15, 2025

    pythongh-137549: handle BaseExceptionGroup in asyncio.Timeout.__aexit__

    f3461d1
  10. ttw225
    added 2 commits that reference this issue on Jul 27, 2026

    Add axis 2: complete classification of all 73 open topic-asyncio issues

    4660903

    Export wave-2 asyncio patches (pythongh-130141 revived + tested, pyth…

    37a54c0
  11. asvetlov
    added 3 commits that reference this issue on Oct 30, 2026

    gh-137549: Handle BaseExceptionGroup in asyncio.Timeout.__aexit__ (#1…

    a683f70

    [3.15] gh-137549: Handle BaseExceptionGroup in asyncio.Timeout.__aexi…

    8ea98fc

    [3.14] gh-137549: Handle BaseExceptionGroup in asyncio.Timeout.__aexi…

    5d615fb

  12. asvetlov commented on Oct 30, 2026

    @asvetlov
    asvetlov
    on Oct 30, 2026
    Contributor

    Fixed

  13. asvetlov
    closed this as completedon Oct 30, 2026
  14. github-project-automation
    moved this from Todo to Done in asyncioon Oct 30, 2026
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stdlibStandard Library Python modules in the Lib/ directorytopic-asynciotype-bugAn unexpected behavior, bug, or error

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