- Optionally installing and adding to PATH a version of Python that is already installed in the runner's tool cache.
- Downloading, installing and adding to PATH an available version of Python from GitHub Releases ([actions/python-versions](https://github.com/actions/python-versions/releases)) if a specific version is not available in the runner's tool cache.
- Failing if a specific version of Python is not preinstalled or available for download.
The `python-version` input is optional. If not supplied, the action will try to resolve the version from the default `.python-version` file. If the `.python-version` file doesn't exist Python/PyPy version from the PATH will be used. The default version of Python/PyPy in PATH varies between runners and can be changed unexpectedly so we recommend always using `setup-python`.
The action will first check the local [tool cache](docs/advanced-usage.md#hosted-tool-cache) for a [semver](https://github.com/npm/node-semver#versions) match. If unable to find a specific version in the tool cache, the action will attempt to download a version of Python from [GitHub Releases](https://github.com/actions/python-versions/releases) and for PyPy from the official [PyPy's dist](https://downloads.python.org/pypy/).
For information regarding locally cached versions of Python/PyPy on GitHub hosted runners, check out [GitHub Actions Virtual Environments](https://github.com/actions/virtual-environments).
The `python-version` input supports the [Semantic Versioning Specification](https://semver.org/) and some special version notations (e.g. `semver ranges`, `x.y-dev syntax`, etc.), for detailed examples please refer to the section: [Using python-version input](docs/advanced-usage.md#using-python-version-input) of the [Advanced usage](docs/advanced-usage.md) guide.
Using `architecture` input it is possible to specify the required Python/PyPy interpreter architecture: `x86` or `x64`. If the input is not specified the architecture defaults to `x64`.
The action has built-in functionality for caching and restoring dependencies. It uses [toolkit/cache](https://github.com/actions/toolkit/tree/main/packages/cache) under the hood for caching dependencies but requires less configuration settings. Supported package managers are `pip`, `pipenv` and `poetry`. The `cache` input is optional, and caching is turned off by default.
The action defaults to searching for a dependency file (`requirements.txt` for pip, `Pipfile.lock` for pipenv or `poetry.lock` for poetry) in the repository, and uses its hash as a part of the cache key. Input `cache-dependency-path` is used for cases when multiple dependency files are used, they are located in different subdirectories or different files for the hash that want to be used.
>**Note:** Restored cache will not be used if the requirements.txt file is not updated for a long time and a newer version of the dependency is available which can lead to an increase in total build time.
>The requirements file format allows for specifying dependency versions using logical operators (for example chardet>=3.0.4) or specifying dependencies without any versions. In this case the pip install -r requirements.txt command will always try to install the latest available package version. To be sure that the cache will be used, please stick to a specific dependency version and update it manually if necessary.
See examples of using `cache` and `cache-dependency-path` for `pipenv` and `poetry` in the section: [Caching packages data](docs/advanced-usage.md#caching-packages-data) of the [Advanced usage](docs/advanced-usage.md) guide.
