typing_inspect is now filled with python version checks for 3.7. The implementation got significantly more complex when differentiating generics at runtime.

3.6 was undocumented, but the OO API was intuitive:

>>> T = typing.Union[int, float]
>>> assert T.__class__ == typing.Union
>>> assert T.__args__ == (int, float)

3.7 is less convenient and less consistent:

>>> T = typing.Union[int, float]
>>> assert T.__class__ == typing._GenericAlias
>>> assert T.__origin__ == typing.Union
>>> L = typing.List[int]
>>> assert L.__class__ == typing._GenericAlias
>>> assert L.__origin__ == list