title: Check if one of variables is set to None
body: <p>I recently had to implement a small check for any variables that might have not been initialized (and their default value is <code>None</code>). I came up with this:</p>
  
  <pre><code>if None in (var1, var2, var3):
      error_out()
  </code></pre>
  
  <p>While, in my eyes, bordering on beautiful, I was wondering - is this a good way to do it? Is this <strong>the</strong> way to do it? Are there any cases in which this would produce some unexpected results?</p>