Free threaded Python support

[fschulze]

I would like to be able to use py313t in the envlist to explicitly run python3.13t as a free-threaded nogil build in addition to py313 which would run python3.13 as an explicitly regular build.

Is there already some way to do that which I missed?

Currently py313t seems to use python.

Related:

• virtualenv is not able to detect free-threading python3.13t pypa/virtualenv#2776

[gaborbernat]

Someone needs to add this functionality first inside virtualenv, or UV if you're ok using tox-uv...

[gaborbernat]

You can always use https://tox.wiki/en/4.21.2/cli_interface.html#tox-run---discover in the meantime to force it...

[ssbarnea]

IMHO that would likely be the most useful tox change to implement because 3.13t is very near and a major source of bugs. Making easy for people to test it with tox would be... very useful.

[gaborbernat]

PR welcome.

[fschulze]

Thanks for the pointer to --discover, that might already be enough for me. Will try later.

[ngoldbaum]

Sorry for duplicating the open issue. Now that virtualenv has done the release this is unblocked.

[ngoldbaum]

I tried running the tox test suite on a free-threaded Python, but that crashes because devpi depends on argon2-cffi-bindings, which itself depends on cffi. I think we'll have to wait on cffi before we can start working on other nodes in tox's dependency tree so we can add free-threaded CI.

Are you open to patches adding support for free-threading without being able to run the tox tests on CI? Or would you prefer to wait until all of tox's dependencies are ready? I'm happy either way, it's straightfoward to work around this with tox --discover.

[gaborbernat]

I'm open to PRs. devpi is a test dependency, there can be a world where we can make the devpi tests skipped for free thread Pythons.