Build and Setup Python
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.
Table of contents
- 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
- Outputs
- Contributing
Basic usage
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@v1
with:
python-version: '3.6'
cache: pip
But if you wish for a more optimized experience you could use inputs exclusive to this action:
- uses: MatteoH2O1999/setup-python@v1
with:
python-version: '3.6'
allow-build: info
cache-build: true
cache: pip
Motivation
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.
But why? It's deprecated: just use a more recent version
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.
But why a dedicated action? Just use ubuntu-20.04 for that 1 job
Once again, that is possible, but that is
- not good practice as editing the main job matrix will not edit the "special" one;
- a pain to maintain as each new deprecated version needs another job to be created.
Guarantees
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.
Known limits
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).
Performance
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:
- Supported by actions/setup-python
- Already installed on runner
ubuntu-latest → ~10swindows-latest → ~20smacos-latest → ~10s
- Available from actions/python-versions
ubuntu-latest → ~20swindows-latest → ~1mmacos-latest → ~30s
- Not supported by actions/setup-python
- Already cached
ubuntu-latest → ~20swindows-latest → ~30smacos-latest → ~30s
- Built from source
ubuntu-latest → ~3m30swindows-latest → ~25mmacos-latest → ~13m
Security guarantees
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.
Inputs
This action supports the following inputs (in bold are the names of the exclusive inputs for this action):
| Input name | Description | Accepted values | Default value |
|---|
| python-version | Version range or exact version of Python or PyPy to use, using SemVer's version range syntax. Reads from .python-version if both this and python-version-file are unset. | pypy3.7, pypy-3.9, 3.5, 2.7.6, ... | None |
| python-version-file | File containing the Python version to use. Reads from .python-version if both this and python-version are unset. | .python-version, path/to/python/version, ... | None |
| cache | Used to specify a package manager for caching in the default directory. | pip, pipenv and poetry | None |
| architecture | The target architecture of the Python or PyPy interpreter. | x64, x86, arm64, ... | None |
| check-latest | Set this option if you want the action to check for the latest available version that satisfies the version spec. | false, true | false |
| token | The token used to authenticate when fetching Python distributions from actions/python-versions. When running this action on github.com, the default value is sufficient. When running on GHES, you can pass a personal access token for github.com if you are experiencing rate limiting. | example: TokenString | github.token |
| cache-dependency-path | Used to specify the path to dependency files. Supports wildcards or a list of file names for caching multiple dependencies. | example: path/to/dependency/files | '' |
| update-environment | Set this option if you want the action to update environment variables. | true, false | true |
| cache-build | Whether to cache the built Python distribution to speed up successive runs. | true, false | false |
| allow-build | Set the behavior of the action when actions/setup-python fails and has to be built from source. | allow, info, warn, error, force | warn |
allow-build input
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.
Outputs
This action will emit the following outputs:
| Output name | Description |
|---|
| python-version | The installed Python or PyPy version. Useful when given a version range as input. |
| cache-hit | A boolean value to indicate a cache entry was found (for pip, pipenv and poetry). |
| python-path | The absolute path to the Python or PyPy executable. |
Contributing
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.
