Handling dependencies that don’t support free-threading

Runtime dependencies that don't support free-threading

Depending on PyYAML - use PyYAML-ft

If your library depends on PyYAML, you will need to take extra care to use it with free-threaded Python. PyYAML currently does not support free-threading and has some thread-safety issues. Its maintainers have decided to not port PyYAML before free-threading and Cython support for it have been more extensively tested.

That's why we've created a fork of PyYAML with support for free-threading called PyYAML-ft. PyYAML users can switch to this fork if they want to test their code with the free-threaded build.

Currently, PyYAML-ft only supports Python 3.13 and 3.13t (i.e. the free-threaded build of 3.13). To switch to it, you can add the following to your requirements.txt:

PyYAML; python_version < '3.13'
PyYAML-ft; python_version >= '3.13'

If you define your dependencies in pyproject.toml, then you can do the following:

dependencies = [
  "PyYAML; python_version<'3.13'",
  "PyYAML-ft; python_version>='3.13'",
]