De-emphaze addfinalizer in favour of ExitStack

[graingert]

now that py2 support is dropped we should discourage addfinalizer and suggest people make their own ExitStack in a yield fixture

@pytest.fixture
def equipments():
    with contextlib.ExitStack() as exit_stack:
        r = []
        for port in ('C1', 'C3', 'C28'):
            equip = connect(port)
            exit_stack.callback(equip.disconnect)
            r.append(equip)
        yield r

[graingert]

now that py2 support is dropped a handy little fixture that might be worth being built in:

@pytest.fixture
def exit_stack():
    with contextlib.ExitStack() as exit_stack:
        yield exit_stack

can be used as:

def test_foo(exit_stack):
    v = exit_stack.enter_context(cm)
    ...
    some_service = Service()
    exit_stack.callback(some_service.disconnect)

or maybe https://docs.pytest.org/en/latest/reference.html#_pytest.fixtures.FixtureRequest could expose an .exit_stack to be used instead of addfinalizer:

@pytest.fixture
def equipments(request):
    r = []
    for port in ('C1', 'C3', 'C28'):
        equip = connect(port)
        request.exit_stack.callback(equip.disconnect)
        r.append(equip)
    return r

[graingert]

or maybe we should discourage addfinalizer entirely and suggest people make their own ExitStack in a yield fixture?

@pytest.fixture
def equipments():
    with contextlib.ExitStack() as exit_stack:
        r = []
        for port in ('C1', 'C3', 'C28'):
            equip = connect(port)
            exit_stack.callback(equip.disconnect)
            r.append(equip)
        yield r

[nicoddemus]

Not sure, addfinalizer is definitely not going anywhere, but I'm not against adding an example of ExitStack + yield fixture to the docs. 👍