new_contents: class CircularQueue:
      class _Node:
          __slots__ = '_element', '_next'
  
          def __init__(self, element):
              self._element = element
              self._next = next
  
      def __init__(self):
          self._tail = None
          self._size = 0
  
      def __len__(self):
          return self._size
  
      def is_empty(self):
          return self._size == 0
  
      def enqueue(self, e):
          node = self._Node(e)
          if self.is_empty():
              self._tail = node
          else:
              node._next = self._tail._next
          self._tail._next = node
          self._size += 1
  
      def dequeue(self):
          if self.is_empty():
              return None
          node = self._tail._next
  
          if node._next == node:
              self._tail = None
          else:
              self._tail._next = node._next
          
          self._size -= 1
          return node._element
  
      def rotate(self):
          if self.is_empty():
              return None
          else:
              self._tail = self._tail._next
  
subject: Add CircularQueue