python双向列表

class Node:
    def __init__(self, data):
        self.data = data
        self.prev = None
        self.next = None

class DoublyCircularLinkedList:
    def __init__(self):
        self.head = None

    def is_empty(self):
        return self.head is None

    def append(self, data):
        new_node = Node(data)
        if self.is_empty():
            self.head = new_node
            self.head.next = self.head
            self.head.prev = self.head
        else:
            tail = self.head.prev
            tail.next = new_node
            new_node.prev = tail
            new_node.next = self.head
            self.head.prev = new_node

    def traverse(self):
        if self.is_empty():
            print("List is empty")
            return
        current = self.head
        while True:
            print(current.data, end=' ')
            current = current.next
            if current == self.head:
                break
        print()

    def remove_last(self):
        if self.is_empty():
            print("List is empty")
            return
        if self.head.next == self.head:  # Only one node
            self.head = None
        else:
            tail = self.head.prev
            second_last = tail.prev
            second_last.next = self.head
            self.head.prev = second_last
            tail.next = tail.prev = None