title: Python 'If not' syntax
body: <p>I'm a bit confused about how/why so many python developers use <code>if not</code> in their conditional statements. </p>
  
  <p>for example, lets say we had a function, </p>
  
  <pre><code>def foo(bar = None):
      if not bar:
          bar = 2
  </code></pre>
  
  <p>But why go about this way? I mean, wouldn't doing <code>if bar != None</code> or <code>if bar is not None</code>be more explicit? What does <code>if not</code> try to say? </p>