自定义元类控制类的实例化行为

Posted 2021-02-12 jt925

# 知识储备 __call__ 方法,对象加括号就默认执行__call__()

# 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)

# 元类内部也应有一个__call__方法，会在类实例化时触发
# Foo(1,2,x=1)  => Foo.__call__(Foo,1,2,x=1)


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)

    def __call__(self, *args, **kwargs):
        # 第一件事：先造一个空对象obj
        obj = object.__new__(self)
        # 第二件事：初始化obj
        self.__init__(obj, *args, **kwargs)
        # 第三件事：返回obj
        return obj


class Chinese(object,metaclass=Mymeta):
    ‘‘‘
    中文类
    ‘‘‘
    country = ‘China‘

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def talk(self):
        print(‘%s is talking‘ % self.name)

obj = Chinese(‘egon‘,age=18)
print(obj.__dict__)