title: Difference between "if x" and "if x is not None"
body: <p>It appears that "if x" is almost like short-hand for the longer "if x is not None" syntax. Are they functionally identical or are there cases where for a given value of x the two would evaluate differently?</p>
  
  <p>I would assume the behavior should also be identical across Python implementations - but if there are subtle differences it would be great to know.</p>