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``.

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.