>>> from abc import *
>>> A = ABCMeta('A', (), {})
>>> A.__module__
'abc'
>>> import pickle, pickletools
>>> pickletools.dis(pickletools.optimize(pickle.dumps(A)))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
_pickle.PicklingError: Can't pickle <class 'abc.A'>: attribute lookup A on abc failed
>>> A.__module__ = None
>>> pickletools.dis(pickletools.optimize(pickle.dumps(A)))
    0: \x80 PROTO      4
    2: \x95 FRAME      15
   11: \x8c SHORT_BINUNICODE '__main__'
   21: \x8c SHORT_BINUNICODE 'A'
   24: \x93 STACK_GLOBAL
   25: .    STOP
highest protocol among opcodes = 4