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setup-python V2

This action sets up a Python environment for use in actions by:

optionally installing and adding to PATH a version of Python that is already installed in the tools cache
downloading, installing and adding to PATH an available version of Python from GitHub Releases (actions/python-versions) if a specific version is not available in the tools cache
failing if a specific version of Python is not preinstalled or available for download
registering problem matchers for error output

What's new

Ability to download, install and set up Python packages from actions/python-versions that do not come preinstalled on runners
- Allows for pinning to a specific patch version of Python without the worry of it ever being removed or changed
Automatic setup and download of Python packages if using a self-hosted runner
Support for pre-release versions of Python

Usage

Basic:

steps:
- uses: actions/checkout@v2
- uses: actions/setup-python@v2
  with:
    python-version: '3.x' # Version range or exact version of a Python version to use, using SemVer's version range syntax
    architecture: 'x64' # optional x64 or x86. Defaults to x64 if not specified
- run: python my_script.py

Matrix Testing:

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        python-version: [ '2.x', '3.x', 'pypy2', 'pypy3' ]
    name: Python ${{ matrix.python-version }} sample
    steps:
      - uses: actions/checkout@v2
      - name: Setup python
        uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.python-version }}
          architecture: x64
      - run: python my_script.py

Exclude a specific Python version:

jobs:
  build:
    runs-on: ${{ matrix.os }}
    strategy:
      matrix:
        os: [ubuntu-latest, macos-latest, windows-latest]
        python-version: [2.7, 3.6, 3.7, 3.8, pypy2, pypy3]
        exclude:
          - os: macos-latest
            python-version: 3.8
          - os: windows-latest
            python-version: 3.6
    steps:
      - uses: actions/checkout@v2
      - name: Set up Python
        uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.python-version }}
      - name: Display Python version
        run: python -c "import sys; print(sys.version)"

Download and set up a version of Python that does not come preinstalled on an image:

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        # in this example, there is a newer version already installed, 3.7.7, so the older version will be downloaded
        python-version: [3.5, 3.6, 3.7.4, 3.8]
    steps:
    - uses: actions/checkout@v2
    - uses: actions/setup-python@v2
      with:
        python-version: ${{ matrix.python-version }}
    - run: python my_script.py

Download and set up an accurate pre-release version of Python:

steps:
- uses: actions/checkout@v2
- uses: actions/setup-python@v2
  with:
    python-version: '3.9.0-beta.4'
- run: python my_script.py

Download and set up the latest available version of Python (includes both pre-release and stable versions):

steps:
- uses: actions/checkout@v2
- uses: actions/setup-python@v2
  with:
    python-version: '3.9.0-alpha - 3.9.0' # SemVer's version range syntax
- run: python my_script.py

Getting started with Python + Actions

Check out our detailed guide on using Python with GitHub Actions.

Available versions of Python

setup-python is able to configure Python from two sources:

Preinstalled versions of Python in the tools cache on GitHub-hosted runners
- For detailed information regarding the available versions of Python that are installed see Supported software.
- For every minor version of Python, expect only the latest patch to be preinstalled.
- If 3.8.1 is installed for example, and 3.8.2 is released, expect 3.8.1 to be removed and replaced by 3.8.2 in the tools cache.
- If the exact patch version doesn't matter to you, specifying just the major and minor version will get you the latest preinstalled patch version. In the previous example, the version spec 3.8 will use the 3.8.2 Python version found in the cache.
Downloadable Python versions from GitHub Releases (actions/python-versions)
- All available versions are listed in the version-manifest.json file.
- If there is a specific version of Python that is not available, you can open an issue here

Hosted Tool Cache

GitHub hosted runners have a tools cache that comes with a few versions of Python + PyPy already installed. This tools cache helps speed up runs and tool setup by not requiring any new downloads. There is an environment variable called RUNNER_TOOL_CACHE on each runner that describes the location of this tools cache and there is where you will find Python and PyPy installed. setup-python works by taking a specific version of Python or PyPy in this tools cache and adding it to PATH.

	Location
Tool Cache Directory	`RUNNER_TOOL_CACHE`
Python Tool Cache	`RUNNER_TOOL_CACHE/Python/*`
PyPy Tool Cache	`RUNNER_TOOL_CACHE/PyPy/*`

GitHub virtual environments are setup in actions/virtual-environments. During the setup, the available versions of Python and PyPy are automatically downloaded, setup and documented.

Specifying a Python version

If there is a specific version of Python that you need and you don't want to worry about any potential breaking changes due to patch updates (going from 3.7.5 to 3.7.6 for example), you should specify the exact major, minor, and patch version (such as 3.7.5)

The only downside to this is that set up will take a little longer since the exact version will have to be downloaded if the exact version is not already installed on the runner due to more recent versions.
MSI installers are used on Windows for this, so runs will take a little longer to set up vs Mac and Linux.

You should specify only a major and minor version if you are okay with the most recent patch version being used.

There will be a single patch version already installed on each runner for every minor version of Python that is supported.
The patch version that will be preinstalled, will generally be the latest and every time there is a new patch released, the older version that is preinstalled will be replaced.
Using the most recent patch version will result in a very quick setup since no downloads will be required since a locally installed version Python on the runner will be used.

Using `setup-python` with a self hosted runner

Python distributions are only available for the same environments that GitHub Actions hosted environments are available for. If you are using an unsupported version of Ubuntu such as 19.04 or another Linux distribution such as Fedora, setup-python will not work. If you have a supported self-hosted runner and you would like to use setup-python, there are a few extra things you need to make sure are set up so that new versions of Python can be downloaded and configured on your runner.

If you are experiencing problems while configuring Python on your self-hosted runner, turn on step debugging to see addition logs.

Windows

Your runner needs to be running with administrator privileges so that the appropriate directories and files can be set up when downloading and installing a new version of Python for the first time.
If your runner is configured as a service, make sure the account that is running the service has the appropriate write permissions so that Python can get installed. The default NT AUTHORITY\NETWORK SERVICE should be sufficient.
You need 7zip installed and added to your PATH so that the downloaded versions of Python files can be extracted properly during first-time setup.
MSI installers are used when setting up Python on Windows. A word of caution as MSI installers update registry settings.
The 3.8 MSI installer for Windows will not let you install another 3.8 version of Python. If setup-python fails for a 3.8 version of Python, make sure any previously installed versions are removed by going to "Apps & Features" in the Settings app.

Linux

The Python packages that are downloaded from actions/python-versions are originally compiled from source in /opt/hostedtoolcache/ with the --enable-shared flag, which makes them non-relocatable.
Create an environment variable called AGENT_TOOLSDIRECTORY and set it to /opt/hostedtoolcache. This controls where the runner downloads and installs tools.
- In the same shell that your runner is using, type export AGENT_TOOLSDIRECTORY=/opt/hostedtoolcache
- A more permanent way of setting the environment variable is to create a .env file in the same directory as your runner and to add AGENT_TOOLSDIRECTORY=/opt/hostedtoolcache. This ensures the variable is always set if your runner is configured as a service.
Create a directory called hostedtoolcache inside /opt.
The user starting the runner must have write permission to the /opt/hostedtoolcache directory. It is not possible to start the Linux runner with sudo and the /opt directory usually requires root privileges to write to. Check the current user and group that the runner belongs to by typing ls -l inside the runners root directory.
The runner can be granted write access to the /opt/hostedtoolcache directory using a few techniques:
- The user starting the runner is the owner, and the owner has write permission
- The user starting the runner is in the owning group, and the owning group has write permission
- All users have write permission
One quick way to grant access is to change the user and group of /opt/hostedtoolcache to be the same as the runners using chown
- sudo chown runner-user:runner-group opt/hostedtoolcache/
If your runner is configured as a service and you run into problems, make sure the user that the service is running as is correct. For more information, you can check the status of your self-hosted runner.

Mac

The same setup that applies to Linux also applies to Mac, just with a different tools cache directory.
Create a directory called /Users/runner/hostedtoolcache
Set the AGENT_TOOLSDIRECTORY environment variable to /Users/runner/hostedtoolcache.
Change the permissions of /Users/runner/hostedtoolcache so that the runner has write access.

Using Python without `setup-python`

setup-python helps keep your dependencies explicit and ensures consistent behavior between different runners. If you use python in a shell on a GitHub hosted runner without setup-python it will default to whatever is in PATH. The default version of Python in PATH vary between runners and can change unexpectedly so we recommend you always use setup-python.

License

The scripts and documentation in this project are released under the MIT License

Contributions

Contributions are welcome! See our Contributor's Guide

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