title: Extending list returns None
body: <p>I want to add a string to a list: </p>
  
  <pre><code>list1 = ['hi','how','are','you','googl']
  ok = 'item22'
  list1 = list1.extend(ok)
  </code></pre>
  
  <p>but it prints <code>None</code>. Why is that?</p>