title: How to get unique values from a python list of objects
body: <p>I have a class:</p>
  
  <pre><code>class Car:
      make
      model
      year
  </code></pre>
  
  <p>I have a list of Cars and want to get a list of unique models among my Cars. </p>
  
  <p>The list is potentially tens of thousands of items. What's the best way to do this?</p>
  
  <p>Thanks.</p>