I use asdf and its Python plugin [1] to install Python interpreter versions.

For managing virtual environments on my preferred shell (Fish), I use (and maintain) VirtualFish [2].

For managing project dependencies, I activate environments via VirtualFish and then use Poetry [3] to update the dependencies within the environments.

[1]: https://github.com/danhper/asdf-python

[2]: http://github.com/justinmayer/virtualfish

[3]: http://python-poetry.org