The dequeue operation is used to delete items from the queue. This method returns the topmost item from the queue and deletes it from the queue. Here is the implementation of the dequeue method:

  def dequeue(self):
    data = self.items.pop()    # delete the topmost item from the queue
    self.size -= 1             # decrement the size of the queue by 1
     return data

The Python list class has a method called pop(). The pop method does the following:

1. Deletes the last item from the list
2. Returns the deleted item from the list back to the user or code that called it

The last item in the list is popped and saved in the data variable. In the last line of the method, the data is returned.

Consider the following figure as our queue implementation, where three elements are added—1, 2, and 3. To perform a dequeue operation, the node with data 1 is removed from the front of the queue as it was added first:

The resulting elements in the queue are shown as follows: