Fix asyncio warnings emitted during pytest

[amosjyng]

I'm basing these changes on https://stackoverflow.com/a/73367187 . Without this change, I get:

nest_asyncio.py:45: DeprecationWarning: There is no current event loop loop = events.get_event_loop_policy().get_event_loop()

[erdewit]

nest_asyncio.py:45: DeprecationWarning: There is no current event loop

I can't reproduce this warning or find it in the asyncio source with Python 3.11.1 How is it triggered?

[amosjyng]

Interesting, so this script triggers it on 3.11.1 for me:

import nest_asyncio
import asyncio

nest_asyncio.apply()

async def hello():
    return "world"

asyncio.new_event_loop().run_until_complete(hello())

But I recommend running this with pytest; running it with Python doesn't output the warning, but the line in the code that does warnings.warn still gets reached.

Commenting out nest_asyncio.apply() resolves the issue.

Are you able to reproduce it now?

[erdewit]

I tried running the snippet with pytest but still can't produce a warning. The pytest environment looks like this:

platform linux -- Python 3.11.1, pytest-7.1.3, pluggy-1.0.0
rootdir: /home/ewald
plugins: anyio-3.6.1, asyncio-0.19.0, flaky-3.7.0, cov-4.0.0, timeout-2.1.0
asyncio: mode=Mode.STRICT

Note that the snippet creates a new (and unpatched) event loop; To run with a patched loop try something such as the following:

import nest_asyncio
import asyncio

async def hello():
    return "world"

loop = asyncio.new_event_loop()
nest_asyncio.apply(loop)
r = loop.run_until_complete(hello())
assert r == 'world'

[amosjyng]

Ah ok, thanks for the heads up! I've changed it to get_event_loop instead.

I've managed to reproduce this issue in a Github test environment, by modifying your test workflow to run with pytest instead in this commit. If you click through to runs such as this one and open up the "Testsuite" section, you should be able to see the warning reproduced:

Please let me know if I can help any further with reproducing the issue! :)

[amosjyng]

Ping, any updates? Seems like others are running into this too :P

[erdewit]

This is fixed slightly differently by patching the event loop policy: https://github.com/erdewit/nest_asyncio/commit/9d46de93f251f717912dd6055ef79b68e80dec26

[amosjyng]

Awesome!