[New-bugs-announce] [issue45996] Worse error from asynccontextmanager in Python 3.10

[Dima Tisnek]

New submission from Dima Tisnek <dimaqq at gmail.com>:

Consider this illegal code:



import logging
from asyncio import sleep, gather, run
from contextlib import asynccontextmanager

@asynccontextmanager
async def foo():
    await sleep(1)
    yield


async def test():
    f = foo()
    await gather(f.__aenter__(), f.__aenter__())

run(test())



If it's ran with Python 3.9, user gets a sensible error:


  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/contextlib.py", line 175, in __aenter__
    return await self.gen.__anext__()
RuntimeError: anext(): asynchronous generator is already running



However, if it's ran with Python 3.10, user gets a cryptic error:


  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/contextlib.py", line 197, in __aenter__
    del self.args, self.kwds, self.func
AttributeError: args



Which makes it harder to pinpoint what's wrong when the stack is complex.
I've hit this with fastapi/starlette/mangum combo and a custom middleware.

----------
components: asyncio
messages: 407799
nosy: Dima.Tisnek, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: Worse error from asynccontextmanager in Python 3.10
type: behavior
versions: Python 3.10, Python 3.11

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45996>
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