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Impossible to specify a metaclass for a Generic class #3720
Description
Not sure if this issue should go here or in https://github.com/python/typing
Below is a contrived example. In the real world I might not actually control the metaclass for Foo or I may be inheriting from some other class that also has a metaclass.
from typing import Generic, TypeVar
class FooMeta(type):
pass
_T = TypeVar('_T')
class Foo(Generic[_T], metaclass=FooMeta):
pass
This passes MyPy just fine, but fails at runtime with:
$ python3.6 test_generics.py
Traceback (most recent call last):
File "test_generics.py", line 8, in <module>
class Foo(Generic[_T], metaclass=FooMeta):
TypeError: metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
Activity
ilevkivskyi commentedon Jul 14, 2017
I think this should be in
typingrather than here. (Also this is unfortunately not an easy problem.)rowillia commentedon Jul 14, 2017
Thanks @ilevkivskyi , moving over there.