day_5.5py

2018-5-5 15:00:25
单例 : 就是对象只有一个
'''

class main(object):

    __instance = None
    def __new__(cls,):
        if cls.__instance ==None:
            cls.__instance = object.__new__(cls)
            return cls.__instance
        else:
            # return 上一次创建的对象的引用
            return cls.__instance

a = main()
print(id(a))
b= main()
print(id(b))