Looks great, thanks for sharing! I'd definitely try this approach.
Do you write default.nix files by hand, or there are some tools to automate the process?
I suppose for a project with a lot of dependencies (one of my current requirements.txt is over 100 SLOC long - almost all deps are on PyPI; haven't checked nixpkgs as I'm stuck with Debian at the moment) it would be somewhat tiresome to check every package and for every missing one list all the dependencies.
Is a Telegram bot that queries the RAE dictionary (Spanish). It doesn't have any documentation yet, though :S
You can look for the project deps code here: https://git.hso.rocks/hso