Fail to (un)pickle class with abc.ABCMeta metaclass (python 2.7)

[AmatanHead]

Hello!

The current code from the master branch fails to work with classes that have the abc.ABCMeta metaclass.

MWE:

class Q(object):
    __metaclass__ = abc.ABCMeta

q = Q()
cloudpickle.loads(cloudpickle.dumps(q))

With python 2.7.3 this yields:

object.__new__(getset_descriptor) is not safe, use getset_descriptor.__new__()

With python 2.7.13:

TypeError: can't pickle wrapper_descriptor objects

[llllllllll]

This probably broke with #102, ping @ssanderson

[ssanderson]

@llllllllll I think this was broken before #102. I tried rolling back and hit a RecursionError with the following test:

    def test_abc(self):
        class AbstractClass(metaclass=abc.ABCMeta):
            pass

        result = pickle_depickle(AbstractClass())

[ssanderson]

The root issue here is actually that ABCMeta uses WeakSet for caching. Should be fixed by #104.

[ssanderson]

@AmatanHead I can't reproduce the exact error from your initial post, but ABCMeta instances generally seem to be working on #104 if you want to give it a try.

[AmatanHead]

Wow! That was blazingly fast and it works! Thanks a lot!