Most Python packages are defined or called from python-packages.nix, but not all. Some are called from all-packages.nix and this can cause trouble when including such package in a Python environment with a different version of the Python interpreter.

The solution is to call all Python packages/modules via python-packages.nix. That also means any callPackage ../path/to/package/default.nix in all-packages.nix needs to be moved to python-packages.nix. Preferably, the Nix expressions would also be using buildPythonPackage and be moved into python-packages.nix but this is not always possible.

List of modules to look at:

• foursuite. I moved it already.
• ecdsa. Removed duplicate.
• numeric. Old, unmaintained, superseeded 10 years ago by numpy. I think we can drop it. The game castle_combat depends on it but is broken as well.
• pyatspi. Only Python 3 available now, but this is not clear since it is in all-packages.nix and not in python-packages.nix. Could you move this, @jgeerds ?
• psyco. Last release from 2007. i686 only, and not used in nixpkgs. Drop it.
• pycups Moved and updated it.
• pyside should use pyside-setup repository to get pip compatible version of pyside and ofcourse move it to python-packages.nix (by @garbas)

I will open a PR soon with some of the changes.

cc @domenkozar @garbas

See also #1819