python 面向对象编程 之 单例模式

单例模式三种实现方式:

单例模式：单例模式是解决系统资源浪费的一种方案，是指一个类实例化后可以多次使用此对象。

单例模式应用场景：数据库操作、日志、后台打印

# settings.py# Host='127.0.01'# Port=8888

#方法一： 利用自定义元类来 控制对象的生成。class Mymeta(type):    def __init__(self, class_name, class_base, class_dic):        '''        :param class_name: 类名        :param class_base: 基类        :param class_dic: 名称空间        '''        obj = self.__new__(self)#创建新的对象        self.__init__(obj, settings.Host, settings.Port)        self.__instance = obj        super(Mymeta, self).__new__(class_name, class_name, class_dic)

    def __call__(self, *args, **kwargs):  # 对象后加括号触发  obj()        if not (args and kwargs):            return self.__instance

        obj = self.__new__(self)        self.__init__(obj, *args, **kwargs)        return obj

class Mysql(metaclass=Mymeta):    def __init__(self, Host, Port):        self.Host = Host        self.Port = Port

# 方法二：利用类的绑定方法

class Mysql:    __instance = None

    def __init__(self, Host, Port):        self.Host = Host        self.Port = Port

    @classmethod    def single(cls, *args, **kwargs):        if not (args and kwargs):            if not cls.__instance:                cls.__instance = cls.__init__(settings.Host, settings.Port)            return cls.__instance

        return cls.__init__(*args, **kwargs)

# 方法三：利用装饰器def single(cls):    _instance = cls.__init__(settings.Host, settings.Port)

    def wrapper(*args, **kwargs):        if not (args and kwargs):            return _instance        return cls.__init__(*args, **kwargs)

    return wrapper

@singleclass Mysql:    def __init__(self, Host, Port):        self.Host = Host        self.Port = Port