This action wraps around actions/setup-python allowing for deprecated CPython versions to be built from source instead of leading to a failure while appearing transparent in all other cases.

• Build and Setup Python
  • Table of contents
  • Basic usage
  • Motivation
    • But why? It's deprecated: just use a more recent version
    • But why a dedicated action? Just use ubuntu-20.04 for that 1 job
  • Guarantees
  • Known limits
  • Performance
  • Security guarantees
  • Inputs
    • allow-build input
  • Outputs
  • FAQ
  • Contributing

For a more complete view on the actions see action.yml or look in the Inputs and Outputs sections. In general you could replace the original action with this one and it should already work (all its supported inputs are also supported in this one):

- uses: MatteoH2O1999/setup-python@v3
  with:
    python-version: '3.6'

But if you wish for a more optimized experience you could use inputs exclusive to this action:

- uses: MatteoH2O1999/setup-python@v3
  with:
    python-version: '3.6'
    allow-build: info
    cache-build: true
    cache: pip

Since the replacement of ubuntu-20.04 with ubuntu-22.04 runner images actions/setup-python no longer supports Python 3.6 for the ubuntu-latest label. This broke a large number of pipelines as Python 3.6 is still widely used.

This made apparent that a way to support deprecated versions was needed.

Yes, in a perfect world that would be the go to solution. Unfortunately, we do not live in that world, so we can't always choose our dependencies. In fact, I would be willing to bet that most deprecated dependencies are there despite the developers, not because of them. That is why this action came about: to offer an easier way to continue supporting deprecated builds even if github does not anymore.

Once again, that is possible, but that is

1. not good practice as editing the main job matrix will not edit the "special" one;
2. a pain to maintain as each new deprecated version needs another job to be created.

The objective of this action is to guarantee that for every major Python version starting from 2.7 at least one specific version can be successfully installed on the ...-latest images using the default architecture.

TLDR: If you use the major version specification (3.6 instead of 3.6.5) without specifying the architecture as shown in Basic usage this action is guaranteed to work (hopefully...😉) on all the ...-latest labels.

Python versions < 3.5 are too difficult to build from source on Windows. For these versions the action tries to use the official installer from python.org. If this fails, the action fails with an appropriate error message. In this case you should request a version for which python.org offers a binary installer, and not just the source code. On the positive side, every version of Python 2.7 has a binary installer so it shouldn't be a problem.

This action at the moment does not support:

• installing multiple Python versions
• building PyPy from source
• building from source in UNIX systems for a different architecture

This actions tries to but does not guarantee to work on any arbitrary pair (python-version, architecture).

The action's performance depends on the runner OS and on whether Python needs to be built, installed, restored from cache or is already installed:

1. Supported by actions/setup-python
   1. Already installed on runner
      1. ubuntu-latest → ~10s
      2. windows-latest → ~20s
      3. macos-latest → ~10s
   2. Available from actions/python-versions
      1. ubuntu-latest → ~20s
      2. windows-latest → ~1m
      3. macos-latest → ~30s
2. Not supported by actions/setup-python
   1. Already cached
      1. ubuntu-latest → ~20s
      2. windows-latest → ~30s
      3. macos-latest → ~30s
   2. Built from source
      1. ubuntu-latest → ~3m30s
      2. windows-latest → ~25m
      3. macos-latest → ~13m

This action is composite and uses the original actions/setup-python and a custom action MatteoH2O1999/build-and-install-python. Both are referenced by commit hash in order to provide better security: if you use this action using its commit hash it will be safe from future malicious edits to the tags.

This action supports the following inputs (in bold are the names of the exclusive inputs for this action):

This action can apply for different behaviors when it tries to install a CPython version not supported by actions/setup-python:

• error this emulates actions/setup-python and throws an error (thus failing the job) if the Python version cannot be downloaded from actions/python-versions;
• warn(default) this will proceed to build the specified version of CPython but will still throw a warning. This was chosen as the default behavior as the user may not know a deprecated version has been requested;
• info this will build from source and only print to the logs the fact that a specific Python version will be built from source;
• allow same as info but does not even print to logs the fact that CPython will be built from source;
• force this will force Python to be built from source regardless of whether actions/setup-python supports it or not.

This action will emit the following outputs:

This is a byproduct of actions/setup-python. If you wish to cache your pip dependencies, you need to have anywhere in your repository a requirements.txt or a pyproject.toml file. The solution in this case is either creating a blank requirements.txt file or stop caching pip (in order to do so simply remove cache: pip from your .yml file).

This action is pretty much only a wrapper for a javascript action. Any issue you might encounter with this action is probably caused by MatteoH2O1999/build-and-install-python. If you wish to contribute, you should do so there.