Multi-inheritance B024

[barney-ellis]

Hi,

The latest release introduced a new error code (B024) which checks that an abc defines abstract methods/properties. I have an abc, A, which has a __call__ abstract method.

class A(metaclass=abc.ABCMeta):

  def __eq__(self, other: Any) -> bool:
      ...

  def __repr__(self) -> str:
      ...

  @abc.abstractmethod
  def __call__(self, ...) -> ...:
      raise NotImplementedError`

I also have a different abc, RandomA which shares A's methods (such as eq) and abstract __call__, but also has a random number generator as an instance variable

class RandomA(A, metaclass=abc.ABCMeta): 

    def __init__(self, rng: Optional[np.random.Generator]) -> None:
        self.rng = rng if rng is not None else np.random.default_rng()

This way I can create child classes which have deterministic or random behaviour.

RandomA now violates B024 as it doesn't define abstract methods, even though it should inherit A's __call__ method right?

[Zac-HD]

Yep, that's a false alarm.

I think in this specific case you don't need to declare the metaclass though, since that should be inherited from A? I could be wrong though.

[barney-ellis]

This passes the flake8 tests, however my IDE (PyCharm) flags a warning that I'm not implementing the __call__ method from A.

[Zac-HD]

Hmm, I think Pycharm is also giving a false alarm there!

Nonetheless, we've got something to fix too. I propose that B024 be disabled for child classes which inherit from anything but abc.ABC - it'll miss some warnings, but still cover the common cases.

[jakkdl]

Yeah that sounds good, and also fixes #278