类的组合

比如有两个类A，类B，用类C把类A和类B组合起来，使得C有A和B的属性方法。

class Turtle:
    def __init__(self,x):
        self.num = x  

class Fish:
    def __init__(self,y):
        self.num = y  

class Pool:
    def __init__(self,x,y):
        self.turtle = Turtle(x)
        self.fish = Fish(y)
    def print_num(self):
        print("水池里有乌龟 %d 只，鱼 %d 只!"%(self.turtle.num,self.fish.num))  

pool = Pool(1,10)
pool.print_num()  

组合结果
水池里有乌龟 1 只，鱼 10 只!