title: how to find most common entry in dictionary of dictionaries in python
body: <p>I have a dictionary that's two levels deep. That is, each key in the first dictionary is a url and the value is another dictionary with each key being words and each value being the number of times the word appeared on that url. It looks something like this:</p>
  
  <pre><code>dic = {
      'http://www.cs.rpi.edu/news/seminars.html': {
          'hyper': 1,
          'summer': 2,
          'expert': 1,
          'koushk': 1,
          'semantic': 1,
          'feedback': 1,
          'sandia': 1,
          'lewis': 1,
          'global': 1,
          'yener': 1,
          'laura': 1,
          'troy': 1,
          'session': 1,
          'greenhouse': 1,
          'human': 1
  
  ...and so on...
  </code></pre>
  
  <p>The dictionary itself is very long and has 25 urls in it, each url having another dictionary as its value with every word found within the url and the number of times its found.</p>
  
  <p>I want to find the word or words that appear in the most different urls in the dictionary. So the output should look something like this:</p>
  
  <blockquote>
    <p>The following words appear x times on y pages: list of words</p>
  </blockquote>