> And finally...well, I have to admit it, but I use Python like a goddamned moron in that I still don't know how to use virutalenv/venv to do proper dev isolation.

I was the same way for quite a while, until I bumped into pyenv-virtualenv[1]. Just install that plugin, and you can do, eg,

    pyenv virtualenv 3.5.1 my-project

to get a virtual environment called `my-project` based off of Python 3.5.1 (assuming that you've installed 3.5.1 via pyenv, of course). Or, you can just do

    pyenv virtualenv my-project

to make a virtualenv called `my-project` based off of the current version of Python that you're using.

Once you do that, pyenv treats `my-project` just as another installation of Python. In fact, `my-project` will show up in the list of installed versions (`pyenv versions`), and you can switch to it:

    pyenv global my-project

(Or you can switch at the local or shell levels. Whichever.)

And voila! You have your own virtual environment that can contain its own list of libraries.

And no, I'm not a shill for the creator of pyenv, I just really like the software.

[1]: https://github.com/yyuu/pyenv-virtualenv