The platform module does not offer to check whether a processor supports the POPCNT or BMI/BMI2 processor instructions. Am I missing something or is it actually missing this feature?

Python's standard library doesn't aim to solve all problems. Python also supports a lot of platforms and CPU architectures. We'd have to implement this on major platforms like BSD, Linux, and Windows as well as other supported platforms like AIX or VMS multiplied by all support CPUs architectures like X86, X86_64, multiple ARMs, ...

This sounds like a feature that can be implemented in a PyPI package.

What would you use this information for, if it were available from Python code?

This feature is needed for a chess GUI application because the Stockfish chess engine is offered in different builds: a build that supports the POPCNT processor instruction and a build that doesn't, a build that supports the BMI/BMI2 processor instruction set, a 32-bit build and a 64-bit build, also a Windows build and a Linux build.

Then the chess GUI application can check if the processor supports the POPCNT instruction or the BMI/BMI2 processor instruction set and can load an appropriate Stockfish build to analyze a chess game or play against a human chess player by using the appropriate Stockfish build for the machine the chess GUI application is running on.

I think your best bet will be to write a small C extension to find out what's supported by the processor.

Unfortunately, I don't know C, only Python.

Your best bet then is probably using a library built for this purpose like https://github.com/workhorsy/py-cpuinfo

Like Christian said, exposing this information in the standard library would be a fairly large maintenance burden for a feature that can't really be actioned upon from pure Python code.

Thanks for letting me know about py-cpuinfo. It is a very good tool. It solves my problem. This Python issue can now be closed as "Won't fix".

Thanks for your understanding Boštjan, closing this as requested.