AttributeError: '_patch' object has no attribute '_exit_stack'

[aikikode]

Setup

I use Python 3.7.8 and the following setup:

# requirements.txt
asynctest==0.13.0
pytest==5.4.3
pytest-asyncio==0.14.0

and the test file

# test.py
import pytest
from asynctest import mock


async def hello():
    return 'HELLO'


@pytest.mark.asyncio
@mock.patch('test.hello')
class TestFetch:
    async def test_will_pass(self, mock_hello):
        mock_hello.return_value = 'OK'
        assert await hello() == 'OK'

    @pytest.mark.parametrize('x',[1, 2])
    async def test_will_fail_on_second_and_further_params(self, mock_hello, x):
        mock_hello.return_value = 'OK'
        assert await hello() == 'OK'

The issue

After I run the tests:
py.test test.py
I get the following stacktrace:

____________________________________________________________________ TestFetch.test_will_fail_on_second_and_further_params[2] _____________________________________________________________________

self = <[AttributeError("'_PatchedGenerator' object has no attribute 'generator'") raised in repr()] _PatchedGenerator object at 0x10cb4a290>

    def __next__(self):
        try:
            with self._limited_patchings_stack():
>               return self.gen.send(None)
E               StopIteration

venv/lib/python3.7/site-packages/asynctest/mock.py:1041: StopIteration

During handling of the above exception, another exception occurred:

kwargs = {'x': 2}, coro = <coroutine object TestFetch.test_will_fail_on_second_and_further_params at 0x10caff170>
task = <Task finished coro=<TestFetch.test_will_fail_on_second_and_further_params() done, defined at /Users/aikikode/tmp/test...hon3.7/site-packages/asynctest/mock.py:113> exception=AttributeError("'_patch' object has no attribute '_exit_stack'")>

    @functools.wraps(func)
    def inner(**kwargs):
        coro = func(**kwargs)
        if coro is not None:
            task = asyncio.ensure_future(coro, loop=_loop)
            try:
>               _loop.run_until_complete(task)

venv/lib/python3.7/site-packages/pytest_asyncio/plugin.py:179:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
../../.pyenv/versions/3.7.8/lib/python3.7/asyncio/base_events.py:587: in run_until_complete
    return future.result()
venv/lib/python3.7/site-packages/asynctest/mock.py:115: in wrapper
    return await coroutine(*args, **kwargs)
venv/lib/python3.7/site-packages/asynctest/mock.py:1044: in __next__
    self._stop_global_patchings()
venv/lib/python3.7/site-packages/asynctest/mock.py:1033: in _stop_global_patchings
    patching.stop()
../../.pyenv/versions/3.7.8/lib/python3.7/unittest/mock.py:1455: in stop
    return self.__exit__(None, None, None)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <asynctest.mock._patch object at 0x10caf5e10>, exc_info = (None, None, None)

    def __exit__(self, *exc_info):
        """Undo the patch."""
        if not _is_started(self):
            raise RuntimeError('stop called on unstarted patcher')

        if self.is_local and self.temp_original is not DEFAULT:
            setattr(self.target, self.attribute, self.temp_original)
        else:
            delattr(self.target, self.attribute)
            if not self.create and (not hasattr(self.target, self.attribute) or
                        self.attribute in ('__doc__', '__module__',
                                           '__defaults__', '__annotations__',
                                           '__kwdefaults__')):
                # needed for proxy objects like django settings
                setattr(self.target, self.attribute, self.temp_original)

        del self.temp_original
        del self.is_local
        del self.target
>       exit_stack = self._exit_stack
E       AttributeError: '_patch' object has no attribute '_exit_stack'

../../.pyenv/versions/3.7.8/lib/python3.7/unittest/mock.py:1435: AttributeError

Investigation

I did some investigation for the possible cause of this issue:

• _exit_stack was added in Python 3.7.8: python/cpython@4057e8f#diff-ff75b1b83c21770847ade91fa5bb2525L1291 It's set upon patch __enter()__ and deleted in __exit()__.
• asynctest uses mock_to_reuse to reuse the same mock object for a coroutine: https://github.com/Martiusweb/asynctest/blob/v0.13.0/asynctest/mock.py#L1088 - if we reuse the coroutine, then patch __enter()__ method is not called and _exit_stack attribute is not set.
• when used in combination with pytest.mark.parametrize it leads to mock __enter()__ being called only once per test case (regardless of number of "subcases" created with parametrisation), but the patch __exit()__ is called after each of the parametrisation "subtests", so only the first "subtest" passes and all other fail.

[ja8zyjits]

Is pinning Python3.7.7 the only fix? Or do we have a workaround?