old_contents: 
  # Definition for singly-linked list with a random pointer.
  class RandomListNode:
      def __init__(self, x):
          self.label = x
          self.next = None
          self.random = None
          
new_contents: 
  # Definition for singly-linked list with a random pointer.
  class RandomListNode:
      
      def __init__(self, x):
          self.label = x
          self.next = None
          self.random = None
      
      def __repr__(self):
          return '[{0}]'.format(self.label)
      
subject: add __repr__