mypkg.nix

{
  buildPythonApplication,
  writeScriptBin,
  someDep,
  python3,
  
  ...
 }
 
 buildPythonApplication {
   name = "somescript";
   version = "1.0.0";
   
   propagatedBuildInputs = [
    someDep
   ];
   
   binScript = writeScriptBin "myscript" ''
   #!${python3.interpreter}
   <some content>
   '';
   
   installPhase = ''
   mkdir -p $out/bin/
   mv ${binScript} $out/bin/
   '';
 }