Test `rustworkx` with free-threaded Python

[IvanIsCoding]

What is the expected enhancement?

Starting with 3.13, we should test rustworkx with https://py-free-threading.github.io/ to make sure it at least work with a single-thread setting. I don't think we should make our data structures thread-safe (that is a lot of overhead).

Of course this will heavily depend on PyO3 and their API offerings. But so far they have made progress on removing the GIL

[IvanIsCoding]

And we are blocked until NumPy releases a new version supporting free threaded Python anyway: https://py-free-threading.github.io/tracking/.

[gulldan]

https://github.com/numpy/numpy/releases/tag/v2.1.0

[apoorvkh]

Would be pertinent, now that Python 3.14t builds are being distributed! And supported by numpy. Thanks!

So you could add a build for 3.14t. And, once Python 3.15 is released, add a build for abi3t. If cp314-abi3.abi3t is ever supported, the builds for cp39-abi3 and cp314-abi3.abi3t would cover all releases.

Note that the build currently fails for 3.14t.

❯ uv venv --python 3.14t
❯ source .venv/bin/activate
❯ uv pip install rustworkx

Traceback

Resolved 2 packages in 292ms
  × Failed to build `rustworkx==0.17.1`
  ├─▶ The build backend returned an error
  ╰─▶ Call to `setuptools.build_meta.build_wheel` failed (exit status: 1)

      [stdout]
      running bdist_wheel

      [stderr]
      ~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/config/pyprojecttoml.py:72: _ExperimentalConfiguration: `[tool.distutils]` in `pyproject.toml`
      is still *experimental* and likely to change in future releases.
        config = read_configuration(filepath, True, ignore_option_errors, dist)
      Traceback (most recent call last):
        File "<string>", line 11, in <module>
          wheel_filename = backend.build_wheel("~/.cache/uv/builds-v0/.tmpCofwIX", {}, None)
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/build_meta.py", line 432, in build_wheel
          return _build(['bdist_wheel'])
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/build_meta.py", line 423, in _build
          return self._build_with_temp_dir(
                 ~~~~~~~~~~~~~~~~~~~~~~~~~^
              cmd,
              ^^^^
          ...<3 lines>...
              self._arbitrary_args(config_settings),
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          )
          ^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/build_meta.py", line 404, in _build_with_temp_dir
          self.run_setup()
          ~~~~~~~~~~~~~~^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/build_meta.py", line 317, in run_setup
          exec(code, locals())
          ~~~~^^^^^^^^^^^^^^^^
        File "<string>", line 10, in <module>
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/__init__.py", line 115, in setup
          return distutils.core.setup(**attrs)
                 ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/_distutils/core.py", line 186, in setup
          return run_commands(dist)
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/_distutils/core.py", line 202, in run_commands
          dist.run_commands()
          ~~~~~~~~~~~~~~~~~^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/_distutils/dist.py", line 1002, in run_commands
          self.run_command(cmd)
          ~~~~~~~~~~~~~~~~^^^^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/dist.py", line 1102, in run_command
          super().run_command(command)
          ~~~~~~~~~~~~~~~~~~~^^^^^^^^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/_distutils/dist.py", line 1020, in run_command
          cmd_obj.ensure_finalized()
          ~~~~~~~~~~~~~~~~~~~~~~~~^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/_distutils/cmd.py", line 135, in ensure_finalized
          self.finalize_options()
          ~~~~~~~~~~~~~~~~~~~~~^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/command/bdist_wheel.py", line 250, in finalize_options
          self._validate_py_limited_api()
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
        File "~/.cache/uv/builds-v0/.tmpCnFbg9/lib/python3.14t/site-packages/setuptools/command/bdist_wheel.py", line 285, in _validate_py_limited_api
          raise ValueError(
          ...<4 lines>...
          )
      ValueError: `py_limited_api='cp39'` not supported. `Py_LIMITED_API` is currently incompatible with `Py_GIL_DISABLED`. See https://github.com/python/cpython/issues/111506.

      hint: This usually indicates a problem with the package or the build environment.

[IvanIsCoding]

After #1521 is merged I plan to revisit this. PyO3 has much better support for free-threaded Python now and NumPy is no longer a blocker.

For 3.14t and 3.15t I am not expecting an ABI, we'll probably need to rebuild on every Python release.

[IvanIsCoding]

There's a chain of PRs needing to be merged but when we get to #1528, I think we'll be very close to shipping 3.14t support.

It might come either in 0.18.x or in the 0.19.x release series.