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             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            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            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