title: Python outputs type 'Nonetype' when try to add to dictionary
body: <p>Here is the code(Running Python 2.7.6):</p>
  
  <pre><code>currency_pairs = {'PPC': 10}
  print currency_pairs
  currency_pairs = currency_pairs.update({'NMC': 50})
  print type (currency_pairs)
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>{'PPC': 10}
  &lt;type 'NoneType'&gt;
  </code></pre>
  
  <p>Why won't Python add to the dictionary?  I don't understand this.  Any thoughts?</p>