title: Python list + list vs. list.append()
body: <p>Today I spent about 20 minutes trying to figure out why 
  this worked as expected:</p>
  
  <pre><code>users_stories_dict[a] = s + [b] 
  </code></pre>
  
  <p>but this would have a <code>None</code> value: </p>
  
  <pre><code>users_stories_dict[a] = s.append(b)
  </code></pre>
  
  <p>Anyone know why the append function does not return the new list? I'm looking for some sort of sensible reason this decision was made; it looks like a Python novice gotcha to me right now.  </p>