title: why is list[-1:1] empty in python?
body: <pre><code>&gt;&gt;&gt;list=[1,2,3]  
  &gt;&gt;&gt;list[1:2]  
  2  
  &gt;&gt;&gt;list[-1:1]  
  []  
  </code></pre>
  
  <p>In python, <code>list[first:last]</code> is <code>return list[first,first+1,...last-1]</code><br>
  but <code>list[-1:1]</code> is return empty, why not include <code>list[-1]</code>?</p>