类的组合使用方法

所谓类的组合就是把直有横向关系几个类放到一起，即把类的实例化放到一个新类里面，不需要使用继承。

class Turtle(object):    def __init__(self,x):        self.num = xclass Fish(object):    def __init__(self,y):        self.num = yclass Pool(object):    def __init__(self,x,y):        self.turtle = Turtle(x)        self.fish   = Fish(y)    def print_num(self):        print("Pool has turtle %d , fish %d" % (self.turtle.num,self.fish.num))if __name__ == '__main__':    pool = Pool(1,10)    pool.print_num()