title: Python - Write a function that takes a string as an argument and displays the letters backward, one per line
body: <p>This is an exercise from "How to think like a Computer Scientist".  I am learning Python/programming and I'm not sure how to do accomplish this task.  </p>
  
  <p>Here is an example in the book that displays the letters forwards, I can't figure out how to get the opposite effect.  Has to use a while-loop.</p>
  
  <pre><code>fruit = 'banana'
  index = 0
  while index &gt; len(fruit):
          letter = fruit[index]
          print letter
          index = index + 1
  </code></pre>