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)