Summary:
Any class that derives from the ABCMeta class doesn't support keyword variable arguments as defined here :https://www.python.org/dev/peps/pep-3115/. 


Expected:
If i define a simple class that derives from ABCMeta that has a kwarg the class should be created (see below

from collections import UserDict
class MyDict(UserDict, bar='baz'):
    pass
dictionary = MyDict()  # Expect this to create a new instance of MyDict.


Actual:

from collections import UserDict
class MyDict(UserDict, bar='baz'):
    pass
dictionary = MyDict()  # This call fails because UserDict inherits from ABCMeta

Traceback (most recent call last):
  File "abc_meta.py", line 4, in <module>
    class MyDict(UserDict, bar='baz'):