责任链模式，子对象都有一个父对象，请求从一级一级从下向顶级父对象传递。
class One(object):
def __init__(self, name, next=None):
super().__init__()
self.name = name
self.next = next
def do(self):
print(self.name, "do")
self.top()
def top(self):
if self.next:
self.next.do()
def main():
one_a = One("a")
one_b = One("b", one_a)
one_c = One("c", one_b)
one_c.do()
if __name__ == '__main__':
main()
