title: Replacing the last three characters in a string if they match a condition
body: <p>I am trying to take a user inputed string and, if it ends with <code>'ion'</code>, replace the last three characters of the string and add an <code>'e'</code>.</p>
  
  <pre><code>def ion2e(s):
      if s[-3:]=='ion':
          print (s[-3:]+'e')
      else:
          print (s)
  </code></pre>