Hands-On Data Structures and Algorithms with Python - Second Edition

The dequeue operation

The other operation that makes our doubly linked list behave as a queue is the dequeue method. This method removes the node at the front of the queue. To remove the first element pointed to by self.head, an if statement is used:

def dequeue(self):     current = self.head          if self.count == 1:              self.count -= 1              self.head = None              self.tail = None          elif self.count > 1:              self.head = self.head.next              self.head.prev = None              self.count -= 1 

current is initialized by pointing it to self.head. If self.count is 1, then it means only one node is in the list and invariably the queue. Thus, to remove the associated node (pointed to by self.head), the self.head and self.tail variables are set to None.

If the queue has many nodes, then ...