python单例模式

'''
单例模式：存的一样的才用单例模式
1 使用类方法
2 装饰器实现
3 使用元类
'''

# import settings
#使用类方法
# class Mysql:
#     __instance=None
#     def __init__(self,ip,port):
#         self.ip=ip
#         self.port=port
#
#     @classmethod
#     def from_conf(cls):
#         if cls.__instance is None:
#             cls.__instance=cls(settings.IP,settings.PORT)
#         return cls.__instance
#
# obj1=Mysql.from_conf()
# obj2=Mysql.from_conf()
#
# print(obj1)
# print(obj2)

# class Mysql:
#     __instance=None
#     def __init__(self,ip,port):
#         self.ip=ip
#         self.port=port
#     @classmethod
#     def from_conf(cls):
#         if cls.__instance is None:
#             cls.__instance=cls(settings.IP,settings.PORT)
#         return cls.__instance

#装饰器实现
def singleton(cls):
    _instance=cls(settings.IP,settings.PORT)
    def wrapper(*args,**kwargs):
        if len(args)==0 and len(kwargs)==0:
            return _instance
        return cls(*args,**kwargs)
    return wrapper

@singleton
class Mysql:
    def __init__(self,ip,port):
        self.ip=ip
        self.port=port

obj1=Mysql()
print(obj1)
obj2=Mysql()
print(obj1)
print(obj2)
obj3=Mysql('1.1.1.1',3306)
print(obj3)

#使用元类实现

# class Mymeta(type):
#       #类传过来，类名，基类，名称空间
#     def __init__(self,class_name,class_bases,class_dic):#类阶段先定义一个默认的，不传值以此为准
#         super().__init__(class_name,class_bases,class_dic)
#         self.__instance=self.__new__(self) #定义一个名称空间
#         self.__init__(self.__instance, settings.IP, settings.PORT) #名称空间传默认值
#
#     def __call__(self, *args, **kwargs):#如果没传值以默认为准(在类定义阶段就创建好了)，如果传值以此为准
#                                            # call则是在对象实例化的时候使用
#         if len(args)==0 and len(kwargs)==0:
#             return self.__instance
#         obj = self.__new__(self) #调用self(mysql类)的__new__方法,创建一个对象的名称空间并将名称空间命名为obj
#         self.__init__(obj, *args, **kwargs)  #将args,kwargs传给obj空间，是obj独有的属性
#         return obj  #返回obj对象
#
#
# class Mysql(object,metaclass=Mymeta):
#     def __init__(self,ip,port):
#         self.ip=ip
#         self.port=port

# obj1=Mysql()
# print(obj1)
# obj2=Mysql()
# print(obj1)
# print(obj2)
# obj3=Mysql('1.1.1.1',3306)
# print(obj3)