I've always found it odd that Python has no built-in version awareness. All it knows is a single installation and a PYTHONPATH, and you fake per-project dependencies by copying everything into a virtualenv. It seems very much bolted-on. (Granted, most other languages don't do it much better.)

I wish you could just install all packages (in multiple versions!) into one place like /usr/lib/pythoncache, and the module loader would then decide which package version to load at import time. You could define your dependencies as usual in reqirements.txt or pyproject.yaml. And you could use either pip or the system package manager to manage the global package cache.