title: Python list.append as an argument
body: <p>Why does the following code give 'None'? How can I resolve this?</p>
  
  <pre><code>def f1(list1):
      f2(list1.append(2))
  
  def f2(list1):
      print(list1)
  
  f1([1])
  </code></pre>
  
  <p>What also doesn't work:</p>
  
  <pre><code>def f1(list1):
      arg1 = list1.append(2) 
      f2(arg1)
  </code></pre>