old_contents: class Difference:
      """
          TODO
      """
  
      def __init__(self):
          pass
          
      def work(self, data):
          """Process the difference between an element in the `data` list and the 
          next one.
          
          :param data: the data to be processed
          :type data: list
          
          :return: the list of differences
          :rtype: list
          """
          
          return [data[i+1] - data[i] for i in range(len(data) - 1)]
  
new_contents: class Difference:
      """TODO"""
  
      def __init__(self):
          pass
          
      def work(self, data):
          """Process the difference between an element in the `data` list and the 
          next one.
          
          :param data: the data to be processed
          :type data: list
          
          :return: the list of differences
          :rtype: list
          """
          
          return [data[i+1] - data[i] for i in range(len(data) - 1)]
  
subject: Remove example from docstring