对象在python中没有属性错误

我是python编程新手,在下面提到的程序中遇到了一个错误。这是一个将节点添加到链表末尾的简单程序。错误表示对象LinkedList没有属性头。请帮我解决这个问题。

class Node:
    def _init_(self, data):
        self.data = data
        self.next = None

class LinkedList:
    def _init_(self):
        self.head=None

    def createNode(self, data):
        newNode = Node(data)
        return newNode

    def insertNodeHelper(self, head, data):
        if(head==None):
            return self.createNode(data)
        head.next = self.insertNodeHelper(head.next,data)
        return head

    def insertNode(self, data):
        self.head = self.insertNodeHelper(self.head,data)

    def printList(self, head):
        if(head==None):
            return;
        print(head.data)
        self.printList(head.next)

    def printLinkedList(self):
        self.printList(self.head)

l = LinkedList()
l.insertNode(12)
l.insertNode(13)
l.insertNode(15)
l.printList()

我收到以下错误:

Message File Name   Line    Position    
Traceback               
    <module>    <module1>   35      
    insertNode  <module1>   21      
AttributeError: 'LinkedList' object has no attribute 'head'