old_contents: # TODO: make element as an abstract class
  class Element:
  
      # TODO: use **kwargs
      def __init__(self, name, position):
          self.element_type = name
          self.s = position
  
new_contents: # TODO: make element as an abstract class
  class Element:
  
      # TODO: use **kwargs
      def __init__(self, name, length):
          self.element_type = name
          self.length = length
  
subject: Add length parameter to an element