{pkgs ? import <nixpkgs> {}, ...}:
pkgs.mkShell {
  nativeBuildInputs = with pkgs; [python39 poetry git];
  shellHook = ''
    [ -e .venv/bin/python3 ] && VENV_FLAG="--upgrade" || VENV_FLAG="--clear"; python3 -m venv $VENV_FLAG .venv
    [ -e .venv/bin/activate ] && source .venv/bin/activate
  '';
}