John DoeJohn Doe

class (object):
    def __init__(self,data):
    	#初始化node
        self.data = data
        self.next = None

    def __repr__(self):
        return str(self.data)

class LinkedList(object):
    def __init__(self):
    	#初始化linkedlist
        self.length = 0
        self.head = None

    def isEmpty(self):
        #判断链表是否为空
        return self.length  == 0

    def get(self,index):
    	#根据索引获取节点值
        index =  index if index > 0 else self.length + index
        if index > self.length or index < 0:
            return None
        node = self.head
        while index:
            node = node.next
            index -= 1
        return node

    def append(self, node):
    	#在链表末添加node
        if isinstance(node,Node):
            pass
        else:
            node =  Node(data=node)

        if self.isEmpty():
            self.head =  node
        else:
            old_head = self.head
            while old_head.next:
                old_head = old_head.next
            old_head.next = node
        self.length += 1
    
    def insert(self,index,value):
    	#在指定位置添加node
        if type(index) is int:
            if index > self.length:
                print("index is out of range")
                return
            else:
                this_node = Node(data=value)
                current_node = self.head

                if index == 0:
                    self.head = this_node
                    this_node.next = current_node
                    return
                else:
                    
                    while index -1:
                        current_node = current_node.next
                        index -= 1
                    
                    this_node.next = current_node.next
                    current_node.next = this_node
                    self.length += 1
                    return  
        else:
            print("index value must be int.")
            return 
    def delete(self,index):
    	#删除指定node
        if type(index) is int:
            if index > self.length:
                print("index is out of range")
                return
            else:
                if index == 0:
                    self.head = self.head.next
                else:
                    current_node = self.head
                    while index-1:
                        current_node = current_node.next
                        index -=1
                    current_node.next = current_node.next.next
                    self.length -= 1
                    return
        else:
            print("index vlaue must be int.")
            return

    def update(self,index,value):
    	#更新指定node
        if type(index) is int:
            if index > self.length:
                print("index out of range")
                return
            else:
                this_node = Node(data=value)
                if index == 0:
                    this_node.next = self.head.next
                    self.head = this_node
                else:
                    current_node = self.head
                    while index - 1:
                        current_node = current_node.next
                        index -= 1
                    this_node.next = current_node.next.next
                    current_node.next = this_node
                    return
        else:
            print("index must be int")
            return
    def get_length(self):
    	#获取链表长度
        current_node = self.head
        if current_node:
            i = 0
            while current_node:
                current_node = current_node.next
                i += 1
            return i
        else:
            return 0
    def clear(self):
    	#清空链表
        self.head = None
        self.length = 0
        print("clear the linked list finished")
    
    def print_linkedlist(self):
    	#打印链表
        if self.isEmpty():
            print("the linkedlist is empty!")
        else:
            node = self.head
            print("head--",node.data,end=' ')
            while node.next:
                node = node.next
                print("-->",node.data,end=' ')
            print("  -->None.linked list finished")

    def __reversed__(self):
    	#反转链表 递归
        def reverse(pre_node,node):
            if pre_node is self.head:
                pre_node.next = None
            if node:
                next_node = node.next
                node.next = pre_node
                return reverse(node,next_node)
            else:
                self.head = pre_node
        
        return reverse(self.head,self.head.next)

if __name__ == '__main__':
    node0 = Node(data="node0")
    node1 = Node(data="node1")
    node2 = Node(data="node2")
    node3 = Node(data="node3")

    linklist = LinkedList()
    linklist.append(node0)
    linklist.append(node1)
    linklist.append(node2)
    linklist.append(node3)
    linklist.print_linkedlist()
    linklist.insert(3,"nodex")
    linklist.print_linkedlist()
    linklist.delete(4)
    linklist.print_linkedlist()    
    linklist.update(2,"update_node2")
    linklist.print_linkedlist()
    print(linklist.get(2)) 
    print(linklist.get_length())  
    linklist.__reversed__()
    linklist.print_linkedlist()