# coding=utf-8


class SingleNode:

    def __init__(self, item):
        self.item = item
        self.next = None


class SingleLinkedList:
    """
    is_empty() 链表是否为空
    print_end_to_head() 从尾到头打印单链表
    append(item) 链表尾部添加元素

    """

    def __init__(self):
        self._head = None

    def is_empty(self):
        return self._head is None

    def append(self, item):
        if self.is_empty():
            self._head = item
        else:
            cur = self._head
            while cur.next:
                cur = cur.next
            cur.next = item

    def print_end_to_head(self):
        """从尾到头打印单链表"""
        if self.is_empty():
            print(None)
            return
        tmp = []
        cur = self._head
        while cur:
            tmp.insert(0, cur)
            cur = cur.next
        for i in tmp:
            print(i.item)

if __name__ == '__main__':
    sl = SingleLinkedList()
    sl.append(SingleNode(1))
    sl.append(SingleNode(2))
    sl.append(SingleNode(3))
    sl.append(SingleNode(4))
    sl.print_end_to_head()