title: What does << do in Python?
body: <p>I solved a problem on Project Euler but it took about 4 minutes to run, which is above the recommended time, so I was looking through the different solutions in the forum.  One of them included the symbol <code>&lt;&lt;</code> in a list comprehension.  This is what it looked like</p>
  
  <pre><code>blist.extend([(i &lt;&lt; 1) + 3 for i in range(num) if alist.get(i)])  
  </code></pre>
  
  <p>I can't find anywhere what exactly this <code>&lt;&lt;</code> symbol does. Can someone help me? </p>