.python-version file is not used to establish the python version

[gg-kialo]

Description:
v4.1.0 introduced a regression where the repo-root .python-version file is no longer used by default to select the python version to install.
The regression was introduced by #450

Reading from .python-version when the python-version input is unset is documented in action.yml -

setup-python/action.yml

Lines 6 to 7 in 00a5248

	python-version:
	description: "Version range or exact version of Python to use, using SemVer's version range syntax. Reads from .python-version if unset."

Action version:
v4.1.0 (regression from v4.0.0)

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:
N/A

Repro steps:
Create a repository with a .python-version file containing 3.10.4 and a workflow containing a setup-python step, e.g.:

name: CI
on: [push]
jobs:
  python:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Install python
        uses: actions/setup-python@v4.0.0

Expected behavior:
setup-python should install 3.10.4 as it is listed in the .python-version file, i.e. the step logs:

Run actions/setup-python@v4
  with:
    token: ***
Resolved  as 3.10.4

This is the behaviour with v4.0.0.

Actual behavior:
setup-python ignores the .python-version file and logs:

Run actions/setup-python@v4
Warning: Neither 'python-version' nor 'python-version-file' inputs were supplied.
Warning: The `python-version` input is not set.  The version of Python currently in `PATH` will be used.

[IvanZosimov]

Hi, @gg-kialo 👋 Thanks for that issue, actually it's not a bug, but a piece of excess information in the documentation. Since v4.1.0 action will check .python-version file either if .python-version file is specified in python-version-path input or if the path that is specified in python-version-path doesn't exist. Sorry for the inconvenience, we're going to fix the documentation as soon as possible.

[gg-kialo]

Would you consider restoring the old behaviour? I've only just gone through all my repos and workflows and removed the with: python-version: xxx lines.
I quite like tooling respecting my toolchain files without me having to tell them to do so (like rust+cargo, nvm, etc.).

[rs-garrick]

Why do we have to add the default filename to our actions in all of our repos? Shouldn't the default behaviour just find the default file?

[IvanZosimov]

Hi, @gg-kialo and @rs-garrick 👋 Thank you for your questions, we took them into consideration and decided to update behavior of the action, take a look at this PR.

[IvanZosimov]

Hi, @ALL, I'm closing this issue now as the PR mentioned above was merged. If you have any additions feel free to ping us.

[OmeGak]

All my CI workflows are still failing since they don't explicitly specify python-version-file. I guess GitHub Actions uses the latest available release of actions/setup-python@v4 (v4.1.0 at the moment) . Is there an ETA for a new release that includes the restored behavior introduced in #465? I'm trying to assess if it's worth to update all my CI workflows or just wait for the new release.

[IvanZosimov]

Hi, @OmeGak 👋 Sorry for the long delay, the new version of setup-python is released.