That's what PyYAML does as well. It uses PEP 518 [1] to specify the dependencies for the build which PyYAML has included Cython [2]. It's just that for previous

That's what PyYAML does as well. It uses PEP 518 [1] to specify the dependencies for the build which PyYAML has included Cython [2]. It's just that for previous releases there was no upper bound here so pip and other tools just selected the latest version which was incompatible. In the past PyYAML included the cythonised .c files in the sdist but as of 5.4.0 they went the PEP 518 route and ensures the client will cythonise them if installing from the sdist. [1] - https://peps.python.org/pep-0518/ https://peps.python.org/pep-0518/ [2] - https://github.com/yaml/pyyaml/blob/release/6.0/pyproject.toml#L2 https://github.com/yaml/pyyaml/blob/release/6.0/pyproject.to...