title: How to add an empty column to a dataframe?
body: <p>What's the easiest way to add an empty column to a pandas <code>DataFrame</code> object?  The best I've stumbled upon is something like</p>
  
  <pre><code>df['foo'] = df.apply(lambda _: '', axis=1)
  </code></pre>
  
  <p>Is there a less perverse method?</p>