title: How can I compare two lists in python and return matches
body: <p>I want to take two lists and find the values that appear in both.</p>
  
  <pre><code>a = [1, 2, 3, 4, 5]
  b = [9, 8, 7, 6, 5]
  
  returnMatches(a, b)
  </code></pre>
  
  <p>would return <code>[5]</code>, for instance.</p>