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wait_for(gather(...)) logs weird error message #73618Description
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2017-02-03.11:25:24.324>
labels = ['type-bug', '3.7', 'expert-asyncio']
title = 'wait_for(gather(...)) logs weird error message'
updated_at = <Date 2017-08-07.23:45:23.642>
user = 'https://github.com/tecki' bugs.python.org fields:
activity = <Date 2017-08-07.23:45:23.642>
actor = 'chris.jerdonek'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2017-02-03.11:25:24.324>
creator = 'Martin.Teichmann'
dependencies = []
files = []
hgrepos = []
issue_num = 29432
keywords = []
message_count = 4.0
messages = ['286858', '287312', '299847', '299878']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'chris.jerdonek', 'yselivanov', 'Martin.Teichmann']
pr_nums = ['73']
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29432'
versions = ['Python 3.4', 'Python 3.5', 'Python 3.6', 'Python 3.7'] Activitytecki commented on Feb 3, 2017 MannequinAuthor More actions when waiting for a gather that times out, everything works as expected, yet a weird error message is logged. To give a minimal example:
import asyncio
@asyncio.coroutine
def main():
try:
sleep = asyncio.sleep(0.2)
yield from asyncio.wait_for(asyncio.gather(sleep),
timeout=0.1)
except asyncio.TimeoutError:
print("timed out: fine")
yield from asyncio.sleep(0.1)asyncio.get_event_loop().run_until_complete(main())
This outputs:
timed out: fine
_GatheringFuture exception was never retrieved
future: <_GatheringFuture finished exception=CancelledError()>
concurrent.futures._base.CancelledError
As you can see, I used the pre-3.5 syntax so I could test whether it works on older systems. No, it doesn't.
I wrote a unit test for this problem, unfortunately I couldn't solve it yet. tecki commented on Feb 8, 2017 MannequinAuthor More actions I added a solution to this problem. I just silence the bad error message by overwriting _GatheringFuture.__del__ to do nothing. This may have undesired side effects, though. cjerdonek commented on Aug 7, 2017 I noticed that the future defined by asyncio.gather(sleep) is in a "pending" state immediately after the asyncio.TimeoutError.
One workaround is to wait for the cancellation to finish:
@asyncio.coroutine
def main():
sleep = asyncio.sleep(0.2)
future = asyncio.gather(sleep)
try:
yield from asyncio.wait_for(future, timeout=0.1)
except asyncio.TimeoutError:
print(f'future: {future}')
try:
yield from future
except asyncio.CancelledError:
print(f'future: {future}')
yield from asyncio.sleep(0.1)asyncio.get_event_loop().run_until_complete(main())
Outputs:
future: <_GatheringFuture pending>
future: <_GatheringFuture finished exception=CancelledError()>
Another option is to pass return_exceptions=True to gather(). This appears to make the log messages you were concerned about go away:
future: <_GatheringFuture pending>
cjerdonek commented on Aug 7, 2017 By the way, I see this exact issue was also raised and discussed here, with a couple responses by Guido, too:
python/asyncio#253 graingert commented on May 31, 2022 it looks like this was fixed in python 3.9:
graingert@superjacent ~/projects python3.9 demo.py
/home/graingert/projects/demo.py:4: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
def main():
timed out: fine
graingert@superjacent ~/projects python3.8 demo.py
demo.py:4: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
def main():
timed out: fine
_GatheringFuture exception was never retrieved
future: <_GatheringFuture finished exception=CancelledError()>
asyncio.exceptions.CancelledError
graingert commented on May 31, 2022 gvanrossum commented on May 31, 2022
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