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):
    pass
 
class 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 = successor
 
class 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 = {&#39;zhangsan&#39;: 78,
          &#39;lisi&#39;: 98,
          &#39;wangwu&#39;: 82,
          &#39;zhaoliu&#39;: 60}
    for name, score in requests.iteritems():
      print &#39;{} is {}&#39;.format(name, h1.handle(score))
 
if __name__== "__main__":
  client = Client()