title: Does this Python expression make sense?
body: <p>I found this kind of expression several times in a python program:</p>
  
  <pre><code>if variable is not None:
      dothings(variable)
  </code></pre>
  
  <p>It seems strange to me, and I think that it has no more sense than:</p>
  
  <pre><code>if variable:
      dothings(variable)
  </code></pre>
  
  <p>Maybe I don't know Python enough, and the expression is explained somewhere?</p>