1 class Dog(object): 2  3     __instance = None   # 设置一个变量来判断储存构造出来得例子 4  5     def __new__(cls): 6         if cls.__instance == None: 7             cls.__instance = object.__new__(cls) 8             return cls.__instance 9         else:10             # return 上一次创建得对象得引用11             return cls.__instance12 13 a = Dog()14 print(id(a))15 b = Dog()16 print(id(b))