How do I install a pip package on a machine without Internet access?

I'm working on a Linux machine without (direct) Internet access. I want to pip install foo for some pypi package foo, but - obviously, that won't work. I have, of course, other machines which are connected the Internet. How would I go about determining what files need to be downloaded, downloading them and installing them once they're on the isolated machine? Notes: * I'd rather get a Python-version-independent answer, but if it is version-dependent, let's assume Python 3.6 or later. * This question sounds the same, but it's actually about installing pip istelf.