> many of the ruby / python packages I want aren't in the nixos-packages repo yet They're not difficult to add. FWIW I've had virtualenvs working pretty well

> many of the ruby / python packages I want aren't in the nixos-packages repo yet They're not difficult to add. FWIW I've had virtualenvs working pretty well on Nix systems - simply provide the environment with the C-dependencies and `virtualenv` from the `pythonPackages` version you desire. Use that `virtualenv` to create your venv directory and you're pretty much away. Oh and you may have to set the `SOURCE_DATE_EPOCH` environment variable. Pretty much works for me. Having said that, the whole concept of virtualenvs and for that matter the whole python packaging ecosystem is a series of rather broken ideas.