title: Python list comprehension issue
body: <p>What am I missing here.</p>
  
  <p>I have a list of dictionaries.</p>
  
  <pre><code>lod = [{'name': 'storm', 'age': 99}]
  </code></pre>
  
  <p>I want to add a key to each item in the list, so i do the following</p>
  
  <pre><code>lod = [r.update({ 'new_key': 'new_value'}) for r in lod]
  </code></pre>
  
  <p>but the resulting lod becomes <code>None</code></p>