This repository contains backports of the CPython `typing` module to earlier versions of

Python. Therefore, code in this repo should follow CPython's style guidelines and

contributors need to sign the PSF Contributor Agreement.

The `typing` module provided by this repository is a backport for Python versions that

do not have `typing` in the standard library: Python 2.7 and 3.4. These versions are no

longer officially supported by CPython, so there is little remaining interest in keeping

the backport up to date. We will accept contributions backporting new features to

`typing`, but we are no longer actively requiring Python 2 support for all

contributions.

The `typing_extensions` module provides a way to access new features from the standard

library `typing` module in older versions of Python. For example, Python 3.10 adds

`typing.TypeGuard`, but users of older versions of Python can use `typing_extensions` to

use `TypeGuard` in their code even if they are unable to upgrade to Python 3.10.

If you contribute the runtime implementation of a new `typing` feature to CPython, you

are encouraged to also implement the feature in `typing_extensions`. Because the runtime

implementation of much of the infrastructure in the `typing` module has changed over

time, this may require different code for some older Python versions.

`typing_extensions` may also include experimental features that are not yet part of the

standard library, so that users can experiment with them before they are added to the

standard library. Such features should ideally already be specified in a PEP or draft

PEP.

`typing_extensions` still supports all Python versions supported by `typing`, down to

Python 2.7 and 3.4. However, it is OK to omit support for Python versions that have

reached end of life if doing so is too difficult or otherwise does not make sense. For

example, `typing_extensions.AsyncGenerator` only exists on Python 3.6 and higher,

because async generators were added to the language in 3.6.

`typing_extensions` and `typing` are usually released together using the same version

numbers. The version number indicates the version of the standard library `typing`

module that is reflected in the backport. For example, `typing_extensions` version

3.10.0.0 includes features from the Python 3.10.0 standard library's `typing` module. A

new release that doesn't include any new standard library features would be called

3.10.0.1.

- Do this for both `typing` and `typing_extensions`

- Run tests under all supported versions. As of April 2021 this includes 2.7, 3.4, 3.5,

3.6, 3.7, 3.8, 3.9.

- On macOS, you can use `pyenv <https://github.com/pyenv/pyenv>`\_ to manage multiple

Python installations. Long story short:

- `xcode-select --install`

- `brew install pyenv`

- `echo 'eval "$(pyenv init -)"' >> ~/.bash_profile`

- Open a new shell

- `pyenv install 3.5.3`

- `pyenv install 3.4.6`

- (assuming you already have 2.7.13 and 3.6.1 from Homebrew)

- `pyenv global system 3.5.3 3.4.6`

- (or some more recent versions)

- You can use `tox` to automate running tests.

- Update the version number in `setup.py`.

- Build the source and wheel distributions:

- `pip3 install -U setuptools wheel`

- `pip2 install -U setuptools wheel`

- `rm -rf dist/ build/`

- `python3 setup.py sdist bdist_wheel`

- `rm -rf build/` (Works around

`a Wheel bug <https://bitbucket.org/pypa/wheel/issues/147/bdist_wheel-should-start-by-cleaning-up>`\_)

- `python2 setup.py bdist_wheel`

- Install the built distributions locally and test (if you were using `tox`, you already

tested the source distribution).

- Make sure twine is up to date, then run `twine upload dist/*`.

- A backport of the `typing` module for older Python versions (2.7 and

* See [CONTRIBUTING.md](/CONTRIBUTING.md) for more.