How to reuse same fixture implementation with different scopes?

[jurisbu]

Hello!

I am looking for a way to reuse same fixture or same fixture implementation in different scopes. I would like to avoid copy-pasting implementation in multiple fixtures with different scopes defined. What would be recommended approach?

So far I have thought about (ab)using yield from as in following example. Not sure if this can lead to some unexpected issues.

@pytest.fixture(session='function')
def my_fixture_fun():
    yield from fixture_impl()

@pytest.fixture(scope='module')
def my_fixture_mod():
    yield from fixture_impl()

@pytest.fixture(scope='session')
def my_fixture_ses():
    yield from fixture_impl()

def fixture_impl():
    # Rather long on complicated fixture implementation here
    print('SETUP: Fixture implmentation')
    yield
    print('TEARDOWN: Fixture implmentation')

Any other ideas or suggestions?
Thanks!

[pytestbot]

GitMate.io thinks possibly related issues are #538 (Fixture scope documentation), #1552 (Suggestion: add new 'parametrization' fixture scope), #2732 (Fixture scope mixing?), #3393 (Customize the fixture ordering on the same scope level), and #668 (autouse fixtures break scope rules).

[RonnyPfannschmidt]

iriginally multi scoped fixtures was planned for pytest 3.0, but it demonstrated impossible to implement without a major refactoring, what you do there is the common workaround, but its suggested to use a contextmanager instead of yield from

[jurisbu]

@RonnyPfannschmidt Thanks for such a prompt response. As per your suggestions of using contexmanager instead, do you mean something along these lines?

@pytest.fixture(scope='module')
def my_fixture_mod():
    with fixture_impl():
        pass


@contextmanager
def fixture_impl():
    print('BEFORE: Fixture implmentation')
    yield
    print('AFTER: Fixture implmentation')

[RonnyPfannschmidt]

@jurisbu correct

with fixture_impl(...) as result:
   yield result

[jurisbu]

Satisfactory answer received. Closing.

[iAnanich]

Same idea can be applied to async fixtures/tests:

@pytest.fixture(scope='module')
async def my_fixture_mod():
    async with fixture_impl() as result:
        yield result


@asynccontextmanager
async def fixture_impl():
    print('BEFORE: Fixture implementation')
    yield
    print('AFTER: Fixture implementation')

[oleg-kondaurov]

@RonnyPfannschmidt @jurisbu @iAnanich Is it possible to somehow trigger the test state to become error or fail in case if an exception is raised in setup or teardown block of the contextmanager?

Current example causes the unhandled exception and pytest process close:

@pytest.fixture(scope='module')
def my_fixture_mod():
    with fixture_impl(...) as result:
       yield result

@contextmanager
def fixture_impl():
    print('raise exception in BEFORE...')
    print(1/0)
    yield
    print('raise exception in AFTER...')
    print(1/0)

[dmos62]

I've been doing this:

def _some_fixture(a_dependency_fixture):
    def __some_fixture(x):
        return x
    yield __some_fixture

some_temp_fixture = pytest.fixture(_some_fixture, scope="function")
some_module_fixture = pytest.fixture(_some_fixture, scope="module")
some_session_fixture = pytest.fixture(_some_fixture, scope="session")

Seemed more straightforward than a context manager. Any downsides to this?

[nicoddemus]

Any downsides to this?

Currently we add an attribute to the function decorated by @pytest.fixture:

pytest/src/_pytest/fixtures.py

Line 1197 in 611b579

function._pytestfixturefunction = self # type: ignore[attr-defined]

So the fixtures above will actually point to the wrong definition... I'm surprised it works.