python 面向对象编程 之 单例模式

单例模式三种实现方式:

# 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)
        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


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