title: List append() in for loop raises exception: 'NoneType' object has no attribute 'append'
body: <p>In Python, trying to do the most basic append function to a list with a loop:
  Not sure what I am missing here:</p>
  <pre><code>a = []
  for i in range(5):    
      a = a.append(i)
  </code></pre>
  <p>returns:</p>
  <blockquote>
  <p>'NoneType' object has no attribute 'append'</p>
  </blockquote>