Typing Extensions – Backported and Experimental Type Hints for Python

The typing module was added to the standard library in Python 3.5 on a
provisional basis and will no longer be provisional in Python 3.7.
However, this means users of Python 3.5 - 3.6 who are unable to upgrade
will not be able to take advantage of new types added to the typing
module, such as typing.Text or typing.Coroutine.

The typing_extensions module contains both backports of these changes as
well as experimental types that will eventually be added to the typing
module, such as Protocol or TypedDict.

Users of other Python versions should continue to install and use the
typing module from PyPi instead of using this one unless specifically
writing code that must be compatible with multiple Python versions or
requires experimental types.