Discover uv-managed Python installations

[edgarrmondragon]

Closes #2901.

This PR updates the interpreter discovery logic to look for uv-managed Python installations.

They currently take priority over Python interpreters in PATH but I'm not 100% sure that makes sense so let me know what you think!

An alternative to this PR that I found after starting work for this PR is implementing a discovery plugin. I see pyenv discovery has not been implemented as a builtin discovery option, so let me know if there are good reasons to also keep uv-managed Pythons outside of virtualenv's scope.

Thanks for contributing, make sure you address all the checklists (for details on how see development documentation)

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

[gaborbernat]

We need to fix the CI first though, can you open a parallel PR for that?

[gaborbernat]

Wrong button 😆

[edgarrmondragon]

We need to fix the CI first though, can you open a parallel PR for that?

Saw you started #2904. Want to take a stab in a different PR?

[gaborbernat]

Yeah I started but solution turned out something complicated... At some point might get back to it.

[esafak]

We need to fix the CI first though, can you open a parallel PR for that?

What's the problem with it?

[gaborbernat]

We need to fix the CI first though, can you open a parallel PR for that?

What's the problem with it?

Seems the way the free threaded Python interpeter was provided broke, and tox can no longer discover it.

[edgarrmondragon]

We need to fix the CI first though, can you open a parallel PR for that?

What's the problem with it?

See https://github.com/pypa/virtualenv/actions/runs/16314042782/job/46075567108.

[edgarrmondragon]

Might not be needed anymore: https://github.com/astral-sh/uv/releases/tag/0.8.0.

[gaborbernat]

Might not be needed anymore: astral-sh/uv@0.8.0 (release).

Can still be helpful as users might not add that folder to their PATH 😊

[nedbat]

I wrote an issue in the tox repo: tox-dev/tox#3580

As workarounds what you can do past make sure you have a compatible Python on your path before uv..

In my case, the uv Python isn't on the PATH at all, yet virtualenv finds it instead of the Python 3.13 that is on the path. Should I open an issue in this repo?

[nedbat]

They currently take priority over Python interpreters in PATH but I'm not 100% sure that makes sense so let me know what you think!

I don't understand the logic of this. If I wanted to use uv interpreters, I would put them in the PATH.

[gaborbernat]

That's not generally true. On Windows we support PEP-514 even without those being on PATH.

In my case, the uv Python isn't on the PATH at all, yet virtualenv finds it instead of the Python 3.13 that is on the path. Should I open an issue in this repo?

If uv takes priority over PATH I'd consider that a bug, and PR/issue welcome.

[nedbat]

If uv takes priority over PATH I'd consider that a bug, and PR/issue welcome.

That's exactly the behavior as explained in the description of this PR.

[edgarrmondragon]

PR here:

• fix: Python in PATH takes precedence over uv-managed Pythons #2952