Please note that I used the tarball from the Python Package Index, not from GitHub. The releases at GitHub don't have a setup.py file, but rather a project.toml file, which I don't know how to handle with the available Python macros.

Same as D2182, the rundeps are not required a builddeps.

builddeps  :
    - pkgconfig(python3)
    - python-setuptools

For future reference, when packaging python stuff, the variable install_requires of the setup.py shows the rundeps (which I'm sure you know), but if the package requires any python builddeps they should be in a variable called setup_requires (when using setuptools at least), and then there's the tests_require deps which are needed as builddeps only if you're including unit testing in your package.yml. See here for lots of useful info!

Thanks for the useful explanation, @EP01 !