old_contents: class Node(object):
      def __init__(self, data, next=None):
          self.data = data
          self.next = next
  
  class Queue(object):
      def __init__(self):
          self.head = None
          self.tail = None
          self._size = 0
  
      def enqueue(self, val):
          pass
  
      def dequeue(self):
          pass
  
new_contents: class Node(object):
      def __init__(self, data, next=None):
          self.data = data
          self.next = next
  
  class Queue(object):
      def __init__(self):
          self.head = None
          self.tail = None
          self._size = 0
  
      def enqueue(self, val):
          temp = Node(val, self.tail)
          self.tail = temp
  
      def dequeue(self):
          pass
  
subject: add enqueue function and passed