title: How to write a function that takes a string and prints the letters in decreasing order of frequency?
body: <p>I got this far:</p>
  
  <pre><code>def most_frequent(string):
      d = dict()
      for key in string:
          if key not in d:
              d[key] = 1
          else:
              d[key] += 1
      return d
  
  print most_frequent('aabbbc')
  </code></pre>
  
  <p>Returning:</p>
  
  <pre><code>{'a': 2, 'c': 1, 'b': 3}
  </code></pre>
  
  <p>Now I need to:</p>
  
  <ol>
  <li>reverse the pair</li>
  <li>sort by number by decreasing order</li>
  <li>only print the letters out</li>
  </ol>
  
  <p>Should I convert this dictionary to tuples or list?</p>