Python packaging is complicated for many reasons (both good and bad), but PyPI's index format is delightfully simple. Projects like this reinforce my opinion that keeping it simple has been a great decision by the Python community and PyPI admins.
In a lot of the worst ways. Dependency resolution can't be done locally, it requires tons of separate network requests to fetch all the requirements.
If I remember it correctly it didn’t expose the python_requires metadata or maybe something to do with extras that to wanted to test. It was definitely an edge case but still something to be aware off.