'''# 知识储备exec()# 参数1：字符串形式的命令# 参数2：全局作用域（字典形式），如果不指定默认就使用globals（）# 参数3：局部作用域（字典形式），如果不指定默认就使用locals（）'''# g = {
    #     'x': 2,#     'y': 4# }# l = {}# exec('''# global x, m# x = 10# m = 100## z = 3# ''', g, l)# print(g)# print(l)'''一切皆对象,元类（产生类的类叫元类，默认用class定义的类，他们的元类是type）'''# 一切皆对象，对象可以怎么用？# 1.都可以被引用，x = obj# 2.都可以当做函数的参数传入# 3.都可以当作函数的返回值# 4.都可以当做容器类型的元素，l = [func, time, obj, l]# # 类也是对象,Foo = type(...)# class Foo:#     pass# obj = Foo()# print(type(obj))# print(type(Foo))# #产生类的类叫元类，默认用class定义的类，他们的元类是type'''定义类'''# 方式一class# class Chinese:#     country = 'china'#     def __init__(self, name):#         self.name = name#     def talk(self):#         print('%s is talking' % self.name)# print(Chinese)# 方式二type#定义类三要素 类名，类的基类， 类的名称空间# class_name = 'Chinese'# class_bases = (object,)# class_body = '''# country = 'china'# def __init__(self, name):#     self.name = name# def talk(self):#     print('%s is talking' % self.name)# '''# class_dic = {}# exec(class_body, globals(), class_dic)# # print(class_dic)## Chinese1 = type(class_name, class_bases, class_dic)# print(Chinese1)'''自定义元类控制类的创建'''# class Mymeta(type):#     def __init__(self, class_name, class_bases, class_dic):#         if not class_name.istitle():#             raise TypeError('类名首字母必须大写')#         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)# class Chinese(object, metaclass = Mymeta):#     '''#     国人#     '''#     country = 'china'#     def __init__(self, name):#         self.name = name#     def talk(self):#         print('%s is talking' % self.name)# c = Chinese('name')# # Chinese = type(class_name, class_bases, class_dic)'''知识储备__call__方法'''# class Foo:#     def __call__(self, *args, **kwargs):#         print(self)#         print(args)#         print(kwargs)# obj = Foo()# obj(1, 2, 3, a=1, b=2, c=3)# 元类内部也应该有一个__call__方法，会在调用Foo时触发执行'''自定义元类控制类的实例化行为'''# class Mymeta(type):#     def __init__(self, class_name, class_bases, class_dic):#         if not class_name.istitle():#             raise TypeError('类名首字母必须大写')#         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)#     def __call__(self, *args, **kwargs):#         # print(self)#         # print(args)#         # print(kwargs)#         # 第一件事，造一个空对象#         obj = object.__new__(self)#         # 第二件事，初始化#         self.__init__(obj, *args, **kwargs)#         # 第三件事，返回obj#         return obj# class Chinese(object, metaclass = Mymeta):#     '''#     国人#     '''#     country = 'china'#     def __init__(self, name):#         self.name = name#     def talk(self):#         print('%s is talking' % self.name)# obj = Chinese('xander')  # Chinese.__call__(Chinese, 'xander')# print(obj.__dict__)'''自定义元类控制类的实例化行为的应用'''# 单例模式# 实现方式一：# class MySQL:#     __instance = None##     def __init__(self):#         self.host = '127.0.0.1'#         self.port = 3306#     @classmethod#     def singleton(cls):#         if not cls.__instance:#             obj = cls()#             cls.__instance = obj#         return cls.__instance# # obj1 = MySQL()# # obj2 = MySQL()# # print(obj1)# # print(obj2)# obj1 = MySQL.singleton()# obj2 = MySQL.singleton()# print(obj1 is obj2)# 实现方式二：元类的方式class Mymeta(type):    def __init__(self, class_name, class_bases, class_dic):        if not class_name.istitle():            raise TypeError('类名首字母必须大写')        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)            self.__instance = obj        return self.__instanceclass Mysql(object, metaclass=Mymeta):    '''单例模式'''    def __init__(self):        self.host = '127.0.0.1'        self.port = 3306    @classmethod    def singleton(cls):        if not cls.__instance:            obj = cls()            cls.__instance = obj        return cls.__instanceobj1 = Mysql()obj2 = Mysql()print(obj1 is obj2)

练习

# 练习一：在元类中控制把自定义类的数据属性都变成大写class Mymate(type):    def __new__(cls, name, args, kwargs):        obj = {}        print(name)        print(args)        print(kwargs)        for a, b in kwargs.items():            if not a.startswith('__'):                obj[a.upper()] = b            else:                obj[a] = b        return type.__new__(cls, name, args, obj)class Chinese(object, metaclass=Mymate):    country = 'chinese'    def talk(self):        print('is talking')print(Chinese.__dict__)# 练习二：在元类中控制自定义的类无需init方法# 1.元类帮其完成创建对象，以及初始化操作；# 2.要求实例化时传参必须为关键字形式，否则抛出异常TypeError: must use keyword argument# 3.key作为用户自定义类产生对象的属性，且所有属性变成大写class Mymate(type):    def __call__(self, *args, **kwargs):        if args:            raise TypeError(':must use keyword argument')        obj = object.__new__(self)  #创建对象，self为类Chinese        for k, v in kwargs.items():            obj.__dict__[k.upper()] = v        return objclass Chinese(object, metaclass=Mymate):    country = 'chinese'    def talk(self):        print('is talking')p = Chinese(name='egon', age=18, sex='male')print(p.__dict__)