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CONTRIBUTING.md

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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.

typing

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.

typing_extensions

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.

Versioning scheme

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.

Workflow for PyPI releases

  • 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/*.