"error: Invalid type" when inheriting from a generic class with not all type variables fixed

[jstasiak]

Code taken straight from typing documentation (https://docs.python.org/3/library/typing.html#typing.Generic):

from typing import TypeVar, Mapping

T = TypeVar('T')

class MyDict(Mapping[str, T]):
    pass

Outcome (with both latest mypy from PyPI and development version):

% python -m mypy qwe.py
qwe.py:5: error: Invalid type "qwe.T"

[rwbarton]

IMO, the example is wrong, and should be class MyDict(Mapping[str, T], Generic[T]): ....

[JukkaL]

In many cases Generic should be optional: https://www.python.org/dev/peps/pep-0484/#arbitrary-generic-types-as-base-classes

Closing as a duplicate of #302.