title: Summing the contents of two collections.Counter() objects
body: <p>I am working with <code>collections.Counter()</code> counters.  I would like to combine two of them in a meaningful manner.</p>
  
  <p>Suppose I have 2 counters, say,  </p>
  
  <pre><code>Counter({'menu': 20, 'good': 15, 'happy': 10, 'bar': 5})
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Counter({'menu': 1, 'good': 1, 'bar': 3})
  </code></pre>
  
  <p>I am trying to end up with:   </p>
  
  <pre><code>Counter({'menu': 21, 'good': 16, 'happy': 10,'bar': 8})
  </code></pre>
  
  <p>How can I do this?</p>