Thanks Fridh! I saw that comment In the python contributing guide, but wasn't sure where to put it instead of python-packages.nix.

I'm also struggling a little to test this. The nox command seems to be dying after trying to build some unrelated Haskell packages in my personal config.nix (that build on their own), and I can't seem to figure out how to get this thing to build in nix-repl. Somehow I did get it to build and put it in my path, and it works for Python 2.7, but I suspect it's busted for Python 3. Is there some set of commands I should be running along the lines of:

nix-shell '<src>' -p "python27Packages.crypto"

Hmm I seem to have busted it. I'll keep trying to figure it out; is there a good representative Python application I should study for reference? Most of the ones I'm looking at (youtube-dl, yapf, isort, flake8, etc.) seem to be in python-packages.nix.

@bhipple good that you gave it a try. Unfortunately you've seen some bad examples so I've forced push the necessary changes instead.

Do you know how I could test this with nix-shell? These seem to work:

$ nix-build -A cryptop
/nix/store/pr3xcl3dy6nzrnw92m4h2yfbv5j041r1-cryptop-0.1.0
$ nix-repl '<src>' 
> :b cryptop
  out -> /nix/store/pr3xcl3dy6nzrnw92m4h2yfbv5j041r1-cryptop-0.1.0

but this one complains about undefined cryptop string:

$ nix-shell --pure '<src>' -p "cryptop"
error: undefined variable 'cryptop' at (string):1:74

Any hints?

Thanks for the help Fridh. Now I can study your fix as the "canonical" example 👍

Answer to the above question in case someone looks at it, courtesy of clever in IRC:

$ nix-shell -E 'with import <src>{}; stdenv.mkDerivation { name="dummy"; buildInputs = [ cryptop ]; }'