old_contents: """Representation of a period of time."""
  
  
  class Period(object):
  
      def __init__(self, start, end):
          self.start = start
          self.end = end
  
      def __repr__(self):
          return "%s-%s" % (self.start, self.end)
  
new_contents: """Representation of a period of time."""
  
  
  class Period(object):
  
      def __init__(self, start, end):
          self.start = start
          self.end = end
  
      def __repr__(self):
          return "%s-%s" % (self.start, self.end)
  
      def __eq__(self, other):
          return ((other.start == self.start) and
                  (other.end == self.end))
  
subject: Add __eq__ method to Period object