链表中倒数第k个节点

class :
    def __init__(self,data=None,next=None):
        self.data=data
        self.next=next  
def output(self,k):
    current = self.head
    n = self.list_len()
    for i in range (0,n-k+1):
        if i == n-k:
            print(current.data)
        current = current.next
    return