Current State of Python Packaging

Typing them one by one is boring so people put the concrete dependencies (with hardcoded versions) in a file and then tell pip: “go read that file and install what’s in there”. For example, if pip can’t find a built version of the dependency you need, it will download the source and build it, basically running setup.py and hoping for the best. In any case, they decided that anybody that want to write their own tool to package should be able to do so, and therefore you need just another meta step to define which packaging system to use and which dependencies you need in order to build your stuff.

Source: stefanoborini.com