title: Advanced list sorting with lambda
body: <p>I've got a list of strings, where each string contains a datestring in the second part, e.g.:</p>
  
  <pre><code>alist = ['foo_20150901', 'bar_20150801', 'baz_20150701']
  </code></pre>
  
  <p>Now I want to have them ordered ascending with respect to the date. I thought this would work like this:</p>
  
  <pre><code>slist = alist.sort(key =(lambda k: int(k.split('_')[-1])))
  </code></pre>
  
  <p>However, printing slist yields <code>None</code>. What's wrong here?</p>