Python的组合模式与责任链模式编程示例

class Trunk(object):  '''树干'''  def __str__(self):    pass  def subtree(self):    passclass Composite(Trunk):  def __init__(self, left=None, right=None, length=None):    self.left=left    self.right=right    self.length=length  def __str__(self):    # 这个结果是在调用subtree()的时候返回    if self.length:      return "(" + self.left.__str__() + ", " + self.right.__str__() + ")" + ": " + str(self.length)     else:      return "(" + self.left.__str__() + ", " + self.right.__str__() + ")"    # 这里其实就是一个技巧，通过这个函数返回下一级的对象，也就是它既是对象还可以是对象的容器    def subtree(self):              return Composite(self.left, self.right)class Leaf(Trunk):  '''叶子类，它没办法继续延伸了'''  def __init__(self, name, length=None):    self.name = name    self.length=length    self.left = None    self.right = None  def __str__(self):    return self.name + ": " + str(self.length)  def subtree(self):    return Leaf(self.name, self.length)if __name__ == "__main__":  # 只有叶子那么就直接返回__str__的拼装结果  t1 = Leaf('A', 0.71399)  print t1  # 有个2个叶子的组合，返回的是2个叶子的对象的组合  t2 = Composite(Leaf('B', -0.00804),     Leaf('C', 0.07470))  print t2  # 这个是嵌套的叶子的组合，树干上面有树枝，树枝上面有叶子  t3 = Composite(Leaf('A', 0.71399),    Composite(Leaf('B', -0.00804),         Leaf('C', 0.07470), 0.1533), 0.0666)  print t3  # 直接通过左右节点找到对应的叶子对象了  t4 = t3.right.right.subtree()  print t4  # t3的左树其实就是叶子对象了  t5 = t3.left.subtree()  print t5

class BaseHandler:  # 它起到了链的作用  def successor(self, successor):    self.successor = successorclass ScoreHandler1(BaseHandler):  def handle(self, request):    if request > 90 and request <= 100:      return "A+"    else:      # 否则传给下一个链，下同，但是我是要return回结果的      return self.successor.handle(request)class ScoreHandler2(BaseHandler):  def handle(self, request):    if request > 80 and request <= 90:      return "A"    else:      return self.successor.handle(request)class ScoreHandler3(BaseHandler):  def handle(self, request):    if request > 70 and request <= 80:      return "B+"    else:      return "unsatisfactory result"class Client:  def __init__(self):    h1 = ScoreHandler1()    h2 = ScoreHandler2()    h3 = ScoreHandler3()    # 注意这个顺序，h3包含一个类似于default结果的东西，是要放在最后的，其他的顺序是无所谓的，比如h1和h2    h1.successor(h2)    h2.successor(h3)    requests = {'zhangsan': 78,          'lisi': 98,          'wangwu': 82,          'zhaoliu': 60}    for name, score in requests.iteritems():      print '{} is {}'.format(name, h1.handle(score))if __name__== "__main__":  client = Client()