title: Pythonic way to iterate over a collections.Counter() instance in descending order?
body: <p>In Python 2.7, I want to iterate over a <code>collections.Counter</code> instance in descending count order. </p>
  
  <pre><code>&gt;&gt;&gt; import collections
  &gt;&gt;&gt; c = collections.Counter()
  &gt;&gt;&gt; c['a'] = 1
  &gt;&gt;&gt; c['b'] = 999
  &gt;&gt;&gt; c
  Counter({'b': 999, 'a': 1})
  &gt;&gt;&gt; for x in c:
          print x
  a
  b
  </code></pre>
  
  <p>In the example above, it appears that the elements are iterated in the order they were added to the Counter instance.  </p>
  
  <p>I'd like to iterate over the list from highest to lowest.  I see that the string representation of Counter does this, just wondering if there's a recommended way to do it.</p>