Don't use `.python-version` for auto-activation

[krystof-k]

Too many issues will kill our team's development velocity, drastically.
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Prerequisite

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Description

• Platform information (e.g. Ubuntu Linux 20.04): macOS Sonoma 14.2.1
• OS architecture (e.g. amd64): arm64
• pyenv version: 2.3.35
• pyenv-virtualenv version: 1.1.5
• Python version: 3.10
• virtualenv version (if installed):
• Please attach the debug log of a faulty Pyenv invocation as a gist

Using .python-version like this

3.10.13/envs/virtualenv

to auto-activate enviroments breaks other tools which do not expect this syntax in .python-version, e.g. GitHub setup-python action:

Warning: Neither 'python-version' nor 'python-version-file' inputs were supplied. Attempting to find '.python-version' file.
Resolved .python-version as 3.10.13/envs/virtualenv
Installed versions
  Version 3.10.13/envs/virtualenv was not found in the local cache
  Error: The version '3.10.13/envs/virtualenv' with architecture 'x64' was not found for Ubuntu 22.04.
  The list of all available versions can be found here: https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json

It would be reasonable not to use .python-version for this or at least use some non-breaking syntax (maybe a comment or something?).

[native-api]

This looks like a problem in the Github action rather than Pyenv.

Moreover, the action's documentation and the error message show a way to override the value from .python-version: with python-version: or python-version-file:.

[krystof-k]

I don't think so, the action or any other tool cannot know of Pyenv syntax.

Unfortunately, there is no official standard for .*-version files, however the common convention is to include only the version number and nothing else. If Pyenv wishes to provide additional configuration options, it would be better to use a different file, such as .pyenvrc, instead of the .python-version file.

[native-api]

Pyenv is the standard for .python-version syntax. It is the software that introduced it.

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Now, a pointer to a virtual environment like the one you gave is actually rather created by a Pyenv plugin, Pyenv-virtualenv.
A pointer like that does specify the base version (as the 1st path component), but the further data only specifies that it's a virtual environment, nothing about its details.

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As such, if you plan to use .python-version in CI, you should either only specify a base version there, or, if you need different settings for local use and for CI, use another setting to govern the CI as specified above.

Alternatively, a CI may choose to support a pointer like that, taking only the base version name (since there's typically no need to make a virtualenv in a CI job).