Python：类的组合

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

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

class Pool:
    def __init__(self,x,y):
        self.turtle=Turtle(x)
        self.fish=Fish(y)
    def print_num(self):
        print('水池里总共有乌龟%d只，小鱼%d条'%(self.turtle.num,self.fish.num))

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