Typing Extensions

The typing_extensions module contains backports of recent changes to the typing module that were not present in older versions of typing.

This module is intended to be used mainly by people who are using Python 3.5+, where the typing module is a part of the standard library and cannot be updated to the latest version on PyPi.

Users of other Python versions should continue to install and use use the typing module from PyPi instead of using this one, unless they are specifically writing code intended to be compatible with multiple versions of Python.

Backported items

This module contains the following backported items:

All Python versions:

• ClassVar
• Collection
• 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 who's 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

There are two different ways to test this module. The first is to simply run each individual Python interpreter against test_typing_extensions.py in the src_py2 and src_py3 folders.

However, because multiple versions of Python for each individual release can be onerous, you can instead run run_tests.py using a single Python interpreter. The run_tests.py file will essentially "modify" the standard library by changing PYTHONPATH to point to individual folders in the test_data repo.

Each individual folder contains a snapshot of the source code for the collections, typing, and abc modules for that given release, letting us test typing against those particular implementations.

run_tests.py will assume that you have Python 3.6.1 and a reasonably modern version of Python 2.7 installed on your system, aliased to py -2.7 and py -3.6 on Windows, and python and python3 on Linux and Mac.