new_contents: class DictDiffer(object):
      """
      Calculate the difference between two dictionaries as:
  
          (1) items added
          (2) items removed
          (3) keys same in both but changed values
          (4) keys same in both and unchanged values
      """
  
      def __init__(self, current_dict, past_dict):
          self.current_dict, self.past_dict = current_dict, past_dict
          self.set_current, self.set_past = set(current_dict.keys()), set(past_dict.keys())
          self.intersect = self.set_current.intersection(self.set_past)
  
      def added(self):
          return self.set_current - self.intersect
  
      def removed(self):
          return self.set_past - self.intersect
  
      def changed(self):
          return set(o for o in self.intersect if self.past_dict[o] != self.current_dict[o])
  
      def unchanged(self):
          return set(o for o in self.intersect if self.past_dict[o] == self.current_dict[o])
  
subject: Add a utility for diffing dicts