链表的定义：
链表(linked list)是由一组被称为结点的数据元素组成的数据结构，每个结点都包含结点本身的信息和指向下一个结点的地址。由于每个结点都包含了可以链接起来的地址信息，所以用一个变量就能够访问整个结点序列。也就是说，结点包含两部分信息：一部分用于存储数据元素的值，称为信息域；另一部分用于存储下一个数据元素地址的指针，称为指针域。链表中的第一个结点的地址存储在一个单独的结点中，称为头结点或首结点。链表中的最后一个结点没有后继元素，其指针域为空。　　

python单链表实现代码：

复制代码 代码如下:
#!/usr/bin/python
# -*- coding: utf-8 -*-

class Node(object):
def __init__(self,val,p=0):
self.data = val
self.next = p

class LinkList(object):
def __init__(self):
self.head = 0

def __getitem__(self, key):

if self.is_empty():
print 'linklist is empty.'
return

elif key <0 or key > self.getlength():
print 'the given key is error'
return

else:
return self.getitem(key)

def __setitem__(self, key, value):

if self.is_empty():
print 'linklist is empty.'
return

elif key <0 or key > self.getlength():
print 'the given key is error'
return

else:
self.delete(key)
return self.insert(key)

def initlist(self,data):

self.head = Node(data[0])

p = self.head

for i in data[1:]:
node = Node(i)
p.next = node
p = p.next

def getlength(self):

p = self.head
length = 0
while p!=0:
length+=1
p = p.next

return length

def is_empty(self):

if self.getlength() ==0:
return True
else:
return False

def clear(self):

self.head = 0

def append(self,item):

q = Node(item)
if self.head ==0:
self.head = q
else:
p = self.head
while p.next!=0:
p = p.next
p.next = q

def getitem(self,index):

if self.is_empty():
print 'Linklist is empty.'
return
j = 0
p = self.head

while p.next!=0 and j <index:
p = p.next
j+=1

if j ==index:
return p.data

else:

print 'target is not exist!'

def insert(self,index,item):

if self.is_empty() or index<0 or index >self.getlength():
print 'Linklist is empty.'
return

if index ==0:
q = Node(item,self.head)

self.head = q

p = self.head
post = self.head
j = 0
while p.next!=0 and j<index:
post = p
p = p.next
j+=1

if index ==j:
q = Node(item,p)
post.next = q
q.next = p

def delete(self,index):

if self.is_empty() or index<0 or index >self.getlength():
print 'Linklist is empty.'
return

if index ==0:
q = Node(item,self.head)

self.head = q

p = self.head
post = self.head
j = 0
while p.next!=0 and j<index:
post = p
p = p.next
j+=1

if index ==j:
post.next = p.next

def index(self,value):

if self.is_empty():
print 'Linklist is empty.'
return

p = self.head
i = 0
while p.next!=0 and not p.data ==value:
p = p.next
i+=1

if p.data == value:
return i
else:
return -1

l = LinkList()
l.initlist([1,2,3,4,5])
print l.getitem(4)
l.append(6)
print l.getitem(5)

l.insert(4,40)
print l.getitem(3)
print l.getitem(4)
print l.getitem(5)

l.delete(5)
print l.getitem(5)

l.index(5)

结果：

5
6
4
40
5
6