Old versions of pip do support Python 2.x. Nothing is preventing you from using them.

There is also a straightforward way of "compiling" your code - install all your dependencies into a virtualenv, tar up that virtualenv, and untar it to the same path on the next system. I've seen this system used to work around pip and Python upgrade complexities that already exist, even within Python 2 alone, and it works fine. Then you're insulated from both changes to pip and changes to the actual packages you're trying to install from pip.

Edit to answer your question because someone downvoted me and now HN is preventing me from replying: I don't think you'll need to do anything special. The common case, honestly, is that you already have some version of pip shipped with your system (e.g., you're using Python and pip from your OS) - just keep using that version, because by definition it's a Python 2-compatible pip. The official Python 2 binaries bundle a version of pip which is also by definition Python 2-compatible.

If you need to upgrade pip for some reason, you might need to specify a version constraint on it, e.g.

    pip install -U 'pip<21'

But you also might not, because there's a way for packages to declare what Python versions they're compatible with, and so pip can take that into account when deciding what to resolve. (The trouble is that very old versions of pip, such as those bundled with LTS-age OSes, don't know how to do that, so they're going to try to upgrade to the newest possible version of pip. Less-old versions of pip running on Python 2 should, I believe, not upgrade to an incompatible version.)