What if the user doesn't have pip installed? This is before we've installed the requirements, so we shouldn't be assuming anything outside the stdlib.

if I'm not mistaken, requirements are parsed out to be installed before installing the desired package, so that should be fine

Isn't that paradoxical? That code is for parsing requirements and those requirements can't be parsed until initial pre-requirements (pip, in this case) are installed.

sorta

from my understanding, when you build the package, your computer extracts the relevant required packages, and sends up that data to pypi, which then in turn sends that data back to users when they install

At least thats how I think it works

I think you may be misunderstanding the problem being discussed. The code that uses pip will crash if pip is not already installed. There is no way to parse and satisfy the dependency on pip, because the author chose to import pip as a library.

pip being a dependency is defined at upload time, it is parsed by the creator of the package, not the consumer, afaik

if you used any other package manager, it would need to resolve dependencies from the additional info in the package index, resulting in pip being downloaded and installed before the desired package is installed

This is actually less robust, since instead of relying on the setuptools API, you now also rely on the pip API.

If you control requirements.txt, there is nothing "not robust" about parsing it in setup.py.