自定义元类控制类的实例化行为的应用

# 单例模式:对一个类多次实例化，但只实例化出同一个对象class Mymeta(type):    def __init__(self,class_name,class_bases,class_dic):        if not class_name.istitle():            raise TypeError(‘类名的首字母必须大写！‘)        if ‘__doc__‘ not in class_dic or not class_dic[‘__doc__‘].strip():            raise TypeError(‘必须有注释，且注释不能为空！‘)        super(Mymeta,self).__init__(class_name,class_bases,class_dic)        self.__instance = None

    def __call__(self, *args, **kwargs):        if not self.__instance:            obj = object.__new__(self)            self.__init__(obj,*args, **kwargs)            self.__instance=obj        return self.__instance

class Mysql(object,metaclass=Mymeta):    ‘‘‘    MYSQL    ‘‘‘    def __init__(self):        self.host=‘127.0.0.1‘        self.port=3306

obj1 = Mysql()obj2 = Mysql()obj3 = Mysql()

print(obj1)print(obj2)print(obj3)

原文地址：https://www.cnblogs.com/jt925/p/10503480.html