[happymellon]

I can't think of anything that Docker would give Python that pyenv and venv wouldn't already.

Not that I wouldn't just use Docker for this, but those two help a lot when dealing with multiple clients who have different versions requirements.

[mynotaccount]

I can give you one example from recent memory: packaging tkinter dev packages with your tkinter python app. Tkinter usually requires some system dependencies on top of python dependencies.