python 设计模式--单例模式

# 单例模式

# 写法一
# class Singleton:
#     def __new__(cls, *args, **kwargs):
#         if not hasattr(cls,"_instance"):
#             cls._instance = super(Singleton,cls).__new__(cls)
#         return cls._instance
#
# class MyClass(Singleton):
#     def __init__(self,a):
#         print("init ~~`")
#         self.a = a
#


# 写法二
class Singleton_02:
    __obj = None
    __initFlag__ = True

    a = 0

    def __new__(cls, *args, **kwargs):
        if cls.__obj == None:
            cls.__obj = object.__new__(cls)
        return cls.__obj

    def __init__(self, a):
        self.a = a
        if Singleton_02.__initFlag__:
            print(‘init~~~‘)
            Singleton_02.__initFlag__ = False


    def GetNumber(self):
        print(self.a)


a1 = Singleton_02(11)
a1.GetNumber()
b = Singleton_02(22)
b.GetNumber()

print(id(a1), id(b))