Python typing library is not provisional in Python 3.7

[Manu Zhang]

Hi all,

I failed to run Python tests in 3.7 with the following error.

  File
"/Users/doria/git/incubator-beam/sdks/python/apache_beam/typehints/native_type_compatibility.py",
line 23, in <module>

    import typing

  File
"/Users/doria/git/incubator-beam/sdks/python/.eggs/typing-3.6.6-py3.7.egg/typing.py",
line 1356, in <module>

    class Callable(extra=collections_abc.Callable, metaclass=CallableMeta):

  File
"/Users/doria/git/incubator-beam/sdks/python/.eggs/typing-3.6.6-py3.7.egg/typing.py",
line 1004, in __new__

    self._abc_registry = extra._abc_registry

AttributeError: type object 'Callable' has no attribute '_abc_registry'

This is because the required typing library is not provisional in Python 3.7
<https://github.com/python/typing#important-dates>.

Any thoughts on this? Shall we add Python 3.7 environment to our tests ?

Thanks,
Manu Zhang