Cannot use typing.Generic with pytypes

Using pytypes 1.0b5:

Python 3.7.3rc1 (default, Mar 13 2019, 11:01:15) 
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import typing
>>> import pytypes
>>> class PCollection(typing.Generic[typing.TypeVar('T')]):
...   pass
... 
>>> PCollection()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/google/home/ehudm/virtualenvs/beam-py37/lib/python3.7/site-packages/pytypes/__init__.py", line 567, in __Generic__new__
    if cls.__origin__ is None:
AttributeError: type object 'PCollection' has no attribute '__origin__'

[udim]

It works on master.

[Stewori]

Also consider My[type(1)](1) or My[pytypes.deep_type(1)](1) to assess the type in more dynamic fashion.