title: Deploy Python app to Heroku with extra pip install
body: <p>I'm trying to implement Deploy to Heroku functionality for my Python application:
  <a href="https://github.com/jet-admin/jet-bridge/tree/heroku" rel="nofollow noreferrer">https://github.com/jet-admin/jet-bridge/tree/heroku</a></p>
  
  <p>It woks OK if just use requirements.txt to install dependencies, but it require me to modify my requirements.txt to include some extra packages that i normally don't need (psycopg2, mysqlclient).</p>
  
  <p>Is it possible not to include all requirements in requirements.txt, but install it with some extra command? I've tried adding postdeploy script which will perform pip install command, but after deploy succed my application says that psycopg2 is not installed (thought i installed it in postdeploy command).</p>