title: Python Module for Distance between UK postcodes
body: <p>I need to calculate distances between UK postcodes. 
  I don't want to use a  web api.
  Does a python module/ library exist for this?
  Or do I have to put together something of my own using data from the <a href="https://www.ordnancesurvey.co.uk/opendatadownload/products.html" rel="nofollow">OrdnanceSurvey</a>? </p>
  
  <p>Thanks,</p>