title: Python inequalities: != vs not ==
body: <p>I realized today while writing some Python that one could write the inequality operator as <code>a!=b</code> or <code>not a==b</code>.  This got me curious:</p>
  
  <ol>
  <li>Do both ways behave exactly the same, or are there some subtle differences?</li>
  <li>Is there any reason to use one over the other?  Is one more commonly used than the other?</li>
  </ol>