title: How to stop collections.Counter from omitting a key if its value is 0?
body: <p>See the problem described <a href="https://stackoverflow.com/questions/31226379/how-to-combine-multiple-dicts-summing-the-values-of-common-keys-and-retaining">here</a>. I want to use collections.Counter, but any key whose sum-of-value amounts to 0 - in this case <strong>d1</strong> - gets omitted:</p>
  
  <pre><code>In [128]: d1 = {'a':1,'b':2,'c':3, 'd':0}
  
  In [129]: d2 = {'b':76}
  
  In [130]: d3 = {'a': 45, 'c':0}
  
  In [131]: from collections import Counter
  
  In [132]: Counter(d1) + Counter(d2) + Counter(d3)
  Out[132]: Counter({'b': 78, 'a': 46, 'c': 3})
  </code></pre>
  
  <p><a href="https://stackoverflow.com/questions/31226379/how-to-combine-multiple-dicts-summing-the-values-of-common-keys-and-retaining">How to combine multiple dicts, summing the values of common keys (and retaining those with value 0) in Python?</a></p>