app.nix

{ tree, runCommand, python3, makeWrapper, fetchFromGitHub, maven, lib, openjdk, writeTextFile, ... }:
let
  app-src =
    builtins.fetchGit {
      url = "ssh://git@github.com/some/pkg";
      rev = "0afc587394dd055be8278a8224aa03be68577kf3";
    };
in
self: super: rec
  app = super.buildPythonPackage rec {
    pname = "app";
    version = "1.0";
    doCheck = false;
    src = app-src;
    buildInputs = with super; [ ];
    propagatedBuildInputs = with super; [ openjdk maven dill pandas ];
  };
  app-exec =
    let
      python = python3.withPackages (ps: with ps; [ app ]);
    in runCommand "app-exec" {
      buildInputs = [ makeWrapper ];
    } ''
      makeWrapper ${python}/bin/python $out --add-flags ${./../../path/to/app.py}
   '';