Build CPython 3.13 by default

[EwoutH]

Enable building with CPython 3.13 by default, no longer requiring prerelease_pythons flag to be set true.

Merge after #1949 is merged.

Builds upon last-year PRs: #1226 and #1565.

[EwoutH]

I see some CI failing. I think one error is the free_threaded 3.13 now being expected to build, but doesn't, so I need to update that test.

The other errors I don't understand directly, so some help with them is appreciated!

Maintainers, feel free to directly modify this PR (push to this branch) by the way.

[EwoutH]

Ah I missed that one, thanks! So far it all looks green.

[EwoutH]

There we go, all green!

[EwoutH]

Thanks for merging!

In what timeframe do you think a new release would be possible?

[henryiii]

If it depends on me, tonight.

[rgommers]

I found that on macOS and Windows it is still necessary to add CIBW_PRERELEASE_PYTHONS: True. Just thought I'd ask here - was that intended?

[henryiii]

No, it shouldn’t be

[henryiii]

Boost-histogram is building 3.13 windows wheels (and macOS both flavors) without the flag, just checked. Is this 3.13 in general or maybe 3.13t? We will be releasing a new patch release of pybind11 with PyMutex, then I’ll be trying that (3.13t) in boost-histogram.

[joerick]

Pyinstrument is building 3.13 without the flag, too.

[rgommers]

Okay, never mind then, it's probably something else (even if adding the env var fixed it for me). And it was regular cp313. For the record:

• failing run
• passing run
• commit that made the difference

[joerick]

You'll need v2.20.0 , you're on 2.19.0 :)

(Or, at least you were in the failing run)

[henryiii]

(2.20 is also the one with the ABI stable Python 3.13rc1)

[rgommers]

Argh, made the updates to 2.20 but missed one indeed, for Windows. And the macOS ones were free-threaded. Sorry for the noise.

[EwoutH]

Now that everyone had about 3 months to get their Python 3.13 wheels building, and 3.13 was released as stable, would this be a good time to talk about building Python 3.13 free-threaded (cp313t) wheels by default?

[neutrinoceros]

Just my two cents but I don't think free-threading wheels should be built by default as long as the feature is considered experimental by CPython developers.

[henryiii]

One thing that might have improved the experience would be if we could detect and enable automatically if the free-threaded classifiers were present. However, the free-threaded classifiers discussion devolved into bike-shedding and died. pypa/trove-classifiers#177 & https://discuss.python.org/t/free-threading-trove-classifier/62406