=================
Typing Extensions
=================
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Overview
========
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.
Users of other Python versions should continue to install and use
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.
Included items
==============
This module currently contains the following:
All Python versions:
--------------------
- ``ClassVar``
- ``ContextManager``
- ``Counter``
- ``DefaultDict``
- ``Deque``
- ``NewType``
- ``NoReturn``
- ``overload`` (note that older versions of ``typing`` only let you use ``overload`` in stubs)
- ``Text``
- ``Type``
- ``TYPE_CHECKING``
Python 3.3+ only:
-----------------
- ``ChainMap``
Python 3.5+ only:
-----------------
- ``AsyncIterable``
- ``AsyncIterator``
- ``AsyncContextManager``
- ``Awaitable``
- ``Coroutine``
Python 3.6+ only:
-----------------
- ``AsyncGenerator``
Other Notes and Limitations
===========================
There are a few types whose interface was modified between different
versions of typing. For example, ``typing.Sequence`` was modified to
subclass ``typing.Reversible`` as of Python 3.5.3.
These changes are _not_ backported to prevent subtle compatibility
issues when mixing the differing implementations of modified classes.
Running tests
=============
To run tests, navigate into the appropriate source directory and run
``test_typing_extensions.py``. You will also need to install the latest
version of ``typing`` if you are using a version of Python that does not
include ``typing`` as a part of the standard library.
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