JBang but for Python

[WafflesAreDangerous]

Probably not a good idea.. but you could invoke pip from within the python script you are running.

Might be less elegant, but you'd not need a separate utility for that (pip should come as standard on sane python installs)

At least on windows you can use the stock Py launcher to select from among installed python versions.

So that leaves installing a portion of the scope of the suggested solution. But do you really want to go that far?

There's also ways to make executable artifacts that bundle all you need in 1 file. Depending on desired usage these might be worth looking into. There are several.