The key difference between pypi and npm is that if you pull a package down and it depends on something==1.0.2 and you depend directly on the incompatible something==0.8.9 both version live together in peace because only request will use 1.0.2. With pypi (and most other dependency management systems) you'll have to make a choice on which one you want to use and in this example you'll have to choose an older version of the library depending on something==1.0.2.