有关下列Python双向链表操作代码的说法错误的是？
class Node:
def __init__(self, Val, Prv = None, Nxt = None):
self.Value = Val
self.Previous, self.Next = Prv, Nxt
def setPrevious(self, Prv = None):
self.Previous = Prv
def setNext(self, Nxt = None):
self.Next = Nxt
firstNode = Node(1)
firstNode.Next = Node(2,firstNode)
firstNode.Next.Next = Node(3,firstNode.Next)
firstNode.Next.setPrevious(firstNode)
firstNode.Next.Next.setPrevious(firstNode.Next)
secondNode = firstNode.Next
firstNode.Next = secondNode.Next
secondNode.Next.Previous = firstNode