Members not listed for ABC-derived classes with custom metaclass

[pkgw]

This issue is an iteration on #52 / #53. Members of a class fail to be listed when the following circumstances hold:

• You're on Python 3
• :inherited-members: is not in effect
• The class inherits from abc.ABC
• None of its superclasses override __slots__
• The class has a metaclass that is not abc.ABCMeta

Sounds incredibly esoteric, but this is biting me in wwt_data_formats right now.

The problem is that the fix for the earlier bug, #53, only tests if the metaclass of the class in question is exactly ABCMeta. If the class uses a custom metaclass that derives from ABCMeta, the check fails. For example:

from abc import ABC, ABCMeta

class IntermediateMeta(ABCMeta):
    pass

class Concrete(ABC, metaclass=IntermediateMeta):
    def mymethod(self):
        """This is a great method."""
        pass

The fix is a one-liner, and I'll submit a PR momentarily.

[pkgw]

BTW, I am working around this by turning on :inherited-members: for now, but it pollutes the namespaces of my classes with lots of extraneous traitlets cruft, so it's really not an acceptable long-term solution.

[simaoafonso-pwt]

#133 is merged, should this be closed?

[pkgw]

Yup!