# 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()

print '\n'.join(['%s:%s' % item for item in obj.__dict__.items()])