Error of "attached to a different loop" appears in 0.11.0 but not in 0.10.0

[krizex]

My testcase get the error of "attached to a different loop" in 0.11.0 but works fine in 0.10.0

The detail is I have the following code in my testcase:

asyncio.get_event_loop().run_in_executor(...)

Is there any related change in 0.11.0?

A simple testcase for reproducing:

import asyncio
import pytest

@pytest.fixture(scope='function')
async def loop():
    return asyncio.get_event_loop()

def foo():
    return 0

@pytest.mark.asyncio
async def test_async(loop):
    await loop.run_in_executor(None, foo)

[simonfagerholm]

@krizex Can you provide the shortest possible example that reproduces this?

[krizex]

@simonfagerholm Thanks for you quick response! Updated the testcase in my original post, please check.

[elemoine]

We're getting hit by the same issue. We need to stick to 0.10.0 for now.

[Gr1N]

Got the same issue with 0.11.0...

[simonfagerholm]

I tested a little bit, it seems the event_loop fixture is not started before the fixture foo in your example. That means that when event_loop is started it will create a new loop to run the test.
The behaviour seems to have changed a bit in the plugin hooks, I suspect pytest_fixture_setup might be the culprit.

By including event_loop as a dependency of foo the example test works.

Also the loop provided by event_loop can be used directly like this:

import pytest

def foo():
    return 0

@pytest.mark.asyncio
async def test_async(event_loop):
    await event_loop.run_in_executor(None, foo)

Would that work as a work around?

[krizex]

The example testcase is just for reproducing the issue. My real use case is not that simple and use asyncio.get_event_loop in some low level module so I could not leverage the event_loop fixture.

At this moment I will stick to v0.10.0 until the issue been fixed.

[simonfagerholm]

Is it possible to make your fixture dependant on the event_loop, i.e add event_loop as an argument to the fixture?

[Gr1N]

It will be not only about tests to rewrite. Because of that you somehow need to pass event_loop fixture in your production code...

[simonfagerholm]

No, as long as the event_loop fixture is started before the production code is executed get_event_loop should return the loop from event_loop

[krizex]

No, the fixture is constructed by calling some low level module and the low level module call asyncio.get_event_loop() to get the event loop. To leverage the event_loop we have to introduce a new param in the code path to pass it to the low level module which is not pratical...

BTW, it is a backward compatibility issue so we have to fix it in the library side.

[krizex]

No, as long as the event_loop fixture is started before the production code is executed get_event_loop should return the loop from event_loop

As you said, why not setup the event_loop fixture by default so this issue can be resolved?

[simonfagerholm]

I agree that it should be fixed, I am just suggesting a work around that if it solves the issue can be implemented.
If it doesn't work my diagnosis is incorrect and further investigation is needed. As I don't have your code causing this problem I cannot try if the diagnosis is correct. Both of my work arounds work in your example.

Also you are free to create a fix and a PR for this issue, if you think you have a solution.

I'm not a maintainer of this project, just your friendly neighborhood sp...programmer, that took some time out of my schedule to help you with a problem