title: Reversal of string.contains In python, pandas
body: <p>I have something like this in my code:</p>
  
  <p><code>df2 = df[df['A'].str.contains("Hello|World")]</code></p>
  
  <p>However, I want all the rows that <em>don't</em> contain either of Hello or World.  How do I most efficiently reverse this?</p>