Having set up my last company doing all development and deployment using nix, moving to a new team which just uses pip/virtualenv and a "bootstrapping script" feels a little unnerving to start with.
The nixpkgs manual has a section on it https://nixos.org/nixpkgs/manual/#sec-python but the key to it is that it's really mostly about managing your PYTHONPATH. You wouldn't typically be installing a python package and just expecting it to be available to a session-launched python invocation (because PYTHONPATH is not exported to the user env of a profile), instead you would probably use nix-shell or a custom-built python environment with the exact package setup you desire...
