Yay I have a PoC of Pants providing Python via Pyenv!

josh@cephandrius:~/work/pants$ which python3.7
josh@cephandrius:~/work/pants$ pyenv versions
* system (set by /home/josh/.pyenv/version)
  3.8.16
josh@cephandrius:~/work/pants$ ./pants run src/python/pants/runme.py
/home/josh/.cache/pants/named_caches/pex_root/venvs/s/9ccfd9b4/venv/bin/python3.7

Note that Pyenv and building Python was completely sandboxed. (Python is still required on the system for a few non-user-code places, but that can be tackled separetly)