CONTRIBUTING.md - third_party/github.com/python/typing_extensions - Git at Google

 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](https://semver.org/). See the documentation
 for more detail.

 ## Development version
 After a release the version is increased once in [pyproject.toml](/pyproject.toml) and
 appended with a `.dev` suffix, e.g. `4.0.1.dev`.
 Further subsequent updates are not planned between releases.

 # Type stubs

 A stub file for `typing_extensions` is maintained
 [in typeshed](https://github.com/python/typeshed/blob/main/stdlib/typing_extensions.pyi).
 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.

 # Linting

 Linting is done via pre-commit. We recommend running pre-commit via a tool such
 as [uv](https://docs.astral.sh/uv/) or [pipx](https://pipx.pypa.io/stable/) so
 that pre-commit and its dependencies are installed into an isolated environment
 located outside your `typing_extensions` clone. Running pre-commit this way
 ensures that you don't accidentally install a version of `typing_extensions`
 from PyPI into a virtual environment inside your `typing_extensions` clone,
 which could easily happen if pre-commit depended (directly or indirectly) on
 `typing_extensions`. If a version of `typing_extensions` from PyPI *was*
 installed into a project-local virtual environment, it could lead to
 unpredictable results when running `typing_extensions` tests locally.

 To run the linters using uv:

 ```
 uvx pre-commit run -a
 ```

 Or using pipx:

 ```
 pipx run pre-commit run -a
 ```

 # Workflow for PyPI releases

 - Make sure you follow the versioning policy in the documentation
   (e.g., release candidates before any feature release, do not release development versions)

 - 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.

 - After the release has been published on PyPI upgrade the version in number in [pyproject.toml](/pyproject.toml) to a `dev` version of the next planned release. For example, change 4.1.1 to 4.X.X.dev, see also [Development versions](#development-version). # TODO decide on major vs. minor increase.
	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](https://semver.org/). See the documentation
	for more detail.

	## Development version
	After a release the version is increased once in [pyproject.toml](/pyproject.toml) and
	appended with a `.dev` suffix, e.g. `4.0.1.dev`.
	Further subsequent updates are not planned between releases.

	# Type stubs

	A stub file for `typing_extensions` is maintained
	[in typeshed](https://github.com/python/typeshed/blob/main/stdlib/typing_extensions.pyi).
	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.

	# Linting

	Linting is done via pre-commit. We recommend running pre-commit via a tool such
	as [uv](https://docs.astral.sh/uv/) or [pipx](https://pipx.pypa.io/stable/) so
	that pre-commit and its dependencies are installed into an isolated environment
	located outside your `typing_extensions` clone. Running pre-commit this way
	ensures that you don't accidentally install a version of `typing_extensions`
	from PyPI into a virtual environment inside your `typing_extensions` clone,
	which could easily happen if pre-commit depended (directly or indirectly) on
	`typing_extensions`. If a version of `typing_extensions` from PyPI was
	installed into a project-local virtual environment, it could lead to
	unpredictable results when running `typing_extensions` tests locally.

	To run the linters using uv:

	```
	uvx pre-commit run -a
	```

	Or using pipx:

	```
	pipx run pre-commit run -a
	```

	# Workflow for PyPI releases

	- Make sure you follow the versioning policy in the documentation
	(e.g., release candidates before any feature release, do not release development versions)

	- 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.

	- After the release has been published on PyPI upgrade the version in number in [pyproject.toml](/pyproject.toml) to a `dev` version of the next planned release. For example, change 4.1.1 to 4.X.X.dev, see also [Development versions](#development-version). # TODO decide on major vs. minor increase.