old_contents: class Node(object):
      def __init__(self, value):
          pass
  
      def value(self):
          pass
  
      def next(self):
          pass
  
  
  class LinkedList(object):
      def __init__(self, values=[]):
          pass
  
      def __len__(self):
          pass
  
      def head(self):
          pass
  
      def push(self, value):
          pass
  
      def pop(self):
          pass
  
      def reversed(self):
          pass
  
  
  class EmptyListException(Exception):
      pass
  
new_contents: class Node(object):
      def __init__(self, value):
          pass
  
      def value(self):
          pass
  
      def next(self):
          pass
  
  
  class LinkedList(object):
      def __init__(self, values=[]):
          self.size = 0
  
      def __len__(self):
          return self.size
  
      def head(self):
          pass
  
      def push(self, value):
          pass
  
      def pop(self):
          pass
  
      def reversed(self):
          pass
  
  
  class EmptyListException(Exception):
      pass
  
subject: implement len