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CONTRIBUTING.md

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Code in this repository should follow CPython's style guidelines and contributors need to sign the PSF Contributor Agreement.

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 already be specified in a PEP or merged into CPython's main branch.

Versioning scheme

Starting with version 4.0.0, typing_extensions uses Semantic Versioning. See the documentation for more detail.

Type stubs

A stub file for typing_extensions is maintained in typeshed. Because of the special status that typing_extensions holds in the typing ecosystem, the stubs are placed in the standard library in typeshed and distributed as part of the stubs bundled with individual type checkers.

Running tests

Testing typing_extensions can be tricky because many development tools depend on typing_extensions, so you may end up testing some installed version of the library, rather than your local code.

The simplest way to run the tests locally is:

  • cd src/
  • python test_typing_extensions.py

Alternatively, you can invoke unittest explicitly:

  • python -m unittest test_typing_extensions.py

Running these commands in the src/ directory ensures that the local file typing_extensions.py is used, instead of any other version of the library you may have installed.

Workflow for PyPI releases

  • Make sure you follow the versioning policy in the documentation (e.g., release candidates before any feature release)

  • Ensure that GitHub Actions reports no errors.

  • Update the version number in typing_extensions/pyproject.toml and in typing_extensions/CHANGELOG.md.

  • Create a new GitHub release at https://github.com/python/typing_extensions/releases/new. Details:

    • The tag should be just the version number, e.g. 4.1.1.
    • Copy the release notes from CHANGELOG.md.

  • Release automation will finish the release. You'll have to manually approve the last step before upload.