title: how to loop down in python list (countdown)
body: <p>how to loop down in python list?</p>
  
  <p>for example</p>
  
  <p>loop:</p>
  
  <pre><code>L = [1,2,3]
  for item in L
      print item #--&gt;1,2,3
  </code></pre>
  
  <p>loop down:</p>
  
  <pre><code>L = [1,2,3]
  for ???
      print item #--&gt;3,2,1
  </code></pre>
  
  <p>thank you</p>