Generate a nix-shell file for Python development.

makepyshell.py

import argparse

def main():
    argparser = argparse.ArgumentParser(
        description = "Generate a nix-shell file (shell.nix) for Python 3.9 development.",
        formatter_class=argparse.ArgumentDefaultsHelpFormatter
    )
    argparser.add_argument("--nix-path", type=str, default="nixpkgs", help="Nix source path.")
    argparser.add_argument("--modules", nargs="+", default=[], help="Python modules for development.")
    args = argparser.parse_args()

    with open("shell.nix", "w") as shellfile:
        shellfile.write("""
{{ pkgs ? import <{0}> {{}} }}:
let
  py = pkgs.python39.withPackages (p: with p; [
    {1}
  ]);
in py.env
""".format(args.nix_path, "\n    ".join(args.modules)))

if __name__ == "__main__":
    main()