为什么在Python中无法获取linkdeque中节点的值？

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

class LinkDeque:
    def __init__(self):
        self.head = None
        self.tail = None

    def append_left(self, value):
        new_node = Node(value)
        if self.head is None:
            self.head = new_node
            self.tail = new_node
        else:
            new_node.next = self.head
            self.head.prev = new_node
            self.head = new_node

    def append_right(self, value):
        new_node = Node(value)
        if self.tail is None:
            self.head = new_node
            self.tail = new_node
        else:
            new_node.prev = self.tail
            self.tail.next = new_node
            self.tail = new_node

    def get_node_values(self):
        values = []
        current = self.head
        while current is not None:
            values.append(current.value)
            current = current.next
        return values

# 示例用法
linkdeque = LinkDeque()
linkdeque.append_left(1)
linkdeque.append_right(2)
linkdeque.append_right(3)
values = linkdeque.get_node_values()
print(values)  # 输出: [1, 2, 3]