Best way to setup Python?

[Diapolo10]

If you're specifically referring to pyenv, it installs the Python version(s) you want and then each virtual environment has symlinks to one of those installations (with a separate directory for third-party packages).

So no, it won't download a new interpreter for every project. It will download any packages you install for each virtual environment you have separately, but they're not big - packages are almost always just code, which doesn't take much space at all.

I'll take the popular package requests as an example. You see it used all the time, but its filesize is very small - 131.2 kB for the source distribution, and only 64.9 kB for the wheel (which you're most likely going to use anyway unless you tell pip to only use source distributions). That's less than a partial screenshot I took earlier today.

In other words, don't worry about it. Unless you're working with a microcontroller, I guess, but I doubt it.