Support Python 3.14

[srittau]

No description provided.

[srittau]

In theory, python-3.14.0-beta.1 is available: https://github.com/actions/python-versions/releases. These might be some caching related issues.

Edit: The manifest hasn't been updated yet: https://github.com/actions/python-versions/blob/main/versions-manifest.json

actions/python-versions#340

[AlexWaygood]

These might be some caching related issues.

We disable the setup-python cache by using the check-latest: true setting in our workflows. So it should be available as soon as the manifest is updated in the python-versions repo

[JelleZijlstra]

This is pretty promising, just need to deal with some new type checker errors.

[srittau]

The only remaining blocker seems to be python/mypy#19020. If a mypy release is planned in the next few days, I think we can wait, otherwise I'd add a step to CI to install mypy from git.

[JelleZijlstra]

Doesn't seem like a release is imminent, probably we should just use mypy main for now

[srittau]

I want to avoid running mypy main if at all possible. This can cause changes unrelated to the Python 3.14, and can have other unforeseen consequences. It also leads to user unfriendly versions in the descriptions of third-party packages.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉