8000 `anext(A(), default)` crashes when `StopAsyncIteration` is raised by a synchronous `__anext__` · Issue #131670 · python/cpython · GitHub
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anext(A(), default) crashes when StopAsyncIteration is raised by a synchronous __anext__ #131670

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picnixz opened this issue Mar 24, 2025 · 5 comments
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anext(A(), default) crashes when StopAsyncIteration is raised by a synchronous __anext__ #131670

picnixz opened this issue Mar 24, 2025 · 5 comments
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interpreter-core (Objects, Python, Grammar, and Parser dirs) type-crash A hard crash of the interpreter, possibly with a core dump

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@picnixz
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picnixz commented Mar 24, 2025 •
edited by bedevere-app bot
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Crash report

What happened?

Python 3.14.0a6+ (heads/main:0e53038ea82, Mar 24 2025, 14:56:34) [GCC 7.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> class A:
...     def __anext__(self):
...         raise StopAsyncIteration
...
>>> anext(A(), "a")
Segmentation fault (core dumped)

There is no crash with anext(A()) or when directly calling __anext__(). Or when __anext__ is declared with async def, it's fine. Or when __anext__() doesn't raise, it's also fine.

NB: I haven't bisected the change but it might be related to what I wrote in 76ffaef.

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Output from running 'python -VV' on the command line:

No response

Linked PRs
@picnixz picnixz added interpreter-core (Objects, Python, Grammar, and Parser dirs) type-crash A hard crash of the interpreter, possibly with a core dump labels Mar 24, 2025
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picnixz commented Mar 24, 2025

cc @kumaraditya303

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sobolevn commented Mar 24, 2025 •
edited
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This happens because awaitable here is NULL:

cpython/Python/bltinmodule.c

Lines 1839 to 1842 in d16f455

awaitable = (*t->tp_as_async->am_anext)(aiterator);
if (default_value == NULL) {
return awaitable;
}

Looks like simple if (awaitable == NULL) check might solve the issue:

» PYTHONFAULTHANDLER=1 ./python.exe ex.py
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/ex.py", line 5, in <module>
    print(anext(A(), "a"))
          ~~~~~^^^^^^^^^^
  File "/Users/sobolev/Desktop/cpython/ex.py", line 3, in __anext__
    raise StopAsyncIteration
StopAsyncIteration

@sobolevn sobolevn self-assigned this Mar 24, 2025
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And not just StopAsyncIteration, but any exception really.

@picnixz
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picnixz commented Mar 24, 2025
8000

Yes, that's what I observed (note that I actually found this bug because it was a typo I made when creating tests for another PR...)

sobolevn added a commit to sobolevn/cpython that referenced this issue Mar 24, 2025
@sobolevn
pythongh-131670: Fix crash in anext() when __anext__ is sync and …
6862fb4 
…raises
@bedevere-app bedevere-app bot mentioned this issue Mar 24, 2025
Merged
sobolevn added a commit that referenced this issue Mar 24, 2025
@sobolevn @picnixz
gh-131670: Fix crash in anext() when __anext__ is sync and raises (…
929afd1 
…#131682)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Mar 24, 2025
@sobolevn @picnixz @miss-islington
pythongh-131670: Fix crash in anext() when __anext__ is sync and …
f6d4fe5 
…raises (pythonGH-131682)

(cherry picked from commit 929afd1)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
miss-islington pushed a commit to miss-islington/cpython that referenced this issue Mar 24, 2025
@sobolevn @picnixz @miss-islington
pythongh-131670: Fix crash in anext() when __anext__ is sync and …
d4189fc 
…raises (pythonGH-131682)

(cherry picked from commit 929afd1)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
This was referenced Mar 24, 2025
Merged
Merged
sobolevn added a commit that referenced this issue Mar 24, 2025
@miss-islington @sobolevn @picnixz
[3.12] gh-131670: Fix crash in anext() when __anext__ is sync and…
76e911a 
… raises (GH-131682) (#131687)

gh-131670: Fix crash in `anext()` when `__anext__` is sync and raises (GH-131682)
(cherry picked from commit 929afd1)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
@picnixz picnixz closed this as completed Mar 24, 2025
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picnixz commented Mar 24, 2025

Thanks for the quick fix Nikita!

sobolevn added a commit that referenced this issue Mar 24, 2025
< 8000 div class="d-flex flex-auto">
@miss-islington @sobolevn @picnixz
[3.13] gh-131670: Fix crash in anext() when __anext__ is sync and…
3492098 
… raises (GH-131682) (#131686)

gh-131670: Fix crash in `anext()` when `__anext__` is sync and raises (GH-131682)
(cherry picked from commit 929afd1)

Co-authored-by: sobolevn <mail@sobolevn.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
diegorusso pushed a commit to diegorusso/cpython that referenced this issue Apr 1, 2025
@sobolevn @picnixz @diegorusso
pythongh-131670: Fix crash in anext() when __anext__ is sync and …
4012974 
…raises (python#131682)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
seehwan pushed a commit to seehwan/cpython that referenced this issue Apr 16, 2025
@sobolevn @picnixz @seehwan80
pythongh-131670: Fix crash in anext() when __anext__ is sync and …
a81b5dc 
…raises (python#131682)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
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