Free threaded classifier?

[henryiii]

Should a classifier be added for free-threading support? It might be obvious if a package provides binaries for free-threaded variants, but it would be nice to declare support for things like build backends and various tooling. Also, it could indicate that a package is actually free-threaded, not just provided binaries. (Maybe two classifiers would be in order? One for supporting free-threading, and one for multithreading)?

[hugovk]

This is being discussed at https://discuss.python.org/t/free-threading-trove-classifier/62406.

[ncoghlan]

Summarising the discussion so far (as of this post): adding multiple classifiers is likely to be worthwhile, allowing projects to indicate the level of maturity of their free threading support.

4 status tiers have been identified so far, different suggested names for some of the tiers are separated by "/":

• Experimental/Unstable: For experimentation and feedback only. Any binary extensions provided for free-threaded builds turn the GIL back on by default.
• Beta: Free threaded usage is supported, but documentation of constraints and limitations may be incomplete. Any binary extensions provided for free-threaded builds leave the GIL disabled.
• Stable/Limited/Limited Support: Free threaded usage is supported, and associated constraints and limitations are documented. Violating the documented constraints may result in segfaults rather than Python exceptions. Any binary extensions provided for free-threaded builds leave the GIL disabled.
• Resilient/Supported: Free threaded usage is supported, and associated constraints and limitations are documented. Violating the documented constraints will reliably give Python exceptions rather than segfaults. Any binary extensions provided for free-threaded builds leave the GIL disabled.

Pure Python packages are permitted to use these classifiers (for example, a pure Python package may add cross-thread locking or subinterpreter invocations such that an underlying Experimental or Beta library effectively becomes Stable or Resilient when used via the free threading support layer).

An explicit numeric ordering (along the lines of that used for Development Stage classifiers) is not currently defined, but potentially could be.

While not specifically covered in the Discourse thread (at time of writing), the suggested prefix for the above would be Free Threading :: (as per python/steering-council#221 (comment) )