title: Sort list while pushing None values to the end
body: <p>I have a homogeneous list of objects with None, but it can contain any type of values. 
  Example:</p>
  
  <pre><code>&gt;&gt;&gt; l = [1, 3, 2, 5, 4, None, 7]
  &gt;&gt;&gt; sorted(l)
  [None, 1, 2, 3, 4, 5, 7]
  &gt;&gt;&gt; sorted(l, reverse=True)
  [7, 5, 4, 3, 2, 1, None]
  </code></pre>
  
  <p>Is there a way without reinventing the wheel to get the list sorted the usual python way, but with None values at the end of the list, like that:</p>
  
  <pre><code>[1, 2, 3, 4, 5, 7, None]
  </code></pre>
  
  <p>I feel like here can be some trick with "key" parameter</p>