Is your feature request related to a problem? Please describe.
In almost all new code I use mypy as one of pre-commit checks. This implies that I want type annotations for all libraries used.

Describe the solution you'd like
I have a PR with type annotations. I even made special efforts to be compatible with Python 3.7 and have no runtime dependency on typing_extensions module. But this solution still incompatible with Python 2.

Describe alternatives you've considered
Alternative is to separate type annotations and make PR to typeshed. Please let me know if you prefer this option, whether you will do this PR yourself or if you want me to do it.