 <p>A simple approach to error-checking user input is with a while loop. For example:</p> <pre><code>def make_score(): while True: score = raw_input('Air, Water, or Grass? ') if score in Attack: break else: print 'Invalid selection.' return score </code></pre> <p>This will loop to input until the user enters a string that matches one of your list items (in the Attack list).</p>