打开Python开发工具IDLE，新建‘DoubleLinkedList.py’文件，并写代码如下;

class Node:

def __init__(self,item):

self.item = item

self.next = None

self.pre = None

class DoubleLinkedList:

def __init__(self):

self.__head = None

def add(self,item):

node = Node(item)

if self.isEmpty():

self.__head = node

else:

node.next = self.__head

self.__head.pre = node

self.__head = node

def isEmpty(self):

return self.__head == None

def walk(self):

cur = self.__head

while cur is not None:

print (cur.item)

cur = cur.next

def length(self):

cur = self.__head

count = 0

while cur is not None:

count += 1

cur = cur.next

return count

if __name__ == '__main__':

sll = DoubleLinkedList()

sll.add(8)

sll.add(9)

sll.walk()

walk、length、isEmpty三个函数和单向链表一样的，不需要改动，add函数要注意pre的赋值。