单例模式:一个类只能创建一个实例 class Singleton(object): def __new__(cls, *args, **kwargs): # print(hasattr(cls,'_instance')) if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls, *args, **kwargs) return cls._instance class MyClass(Singleton): a = 1 my_cls对象的a属性修改之后,my_cls2的属性也随之修改 my_cls = MyClass() my_cls.a = my_cls.a+1 print(my_cls.a) my_cls2 = MyClass() print(my_cls,my_cls2) print(my_cls2.a)