title: How do I add a path to PYTHONPATH in virtualenv
body: <p>I am trying to add a path to the PYTHONPATH environment variable, that would be only visible from a particular virtualenv environment. </p>
  
  <p>I tried <code>SET PYTHONPATH=...</code> under a virtualenv command prompt, but that sets the variable for the whole environment.</p>
  
  <p>How do I achieve that?</p>