3.3

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 MyMeta(type):
    def __new__(cls, class_name, class_bases, class_dic):
        update_attrs = {}
        for i in class_dic:
            if not callable(class_dic[i]) and not i.startswith('__'):
                update_attrs[i.upper()] = class_dic[i]
            else:
                update_attrs[i] = class_dic[i]
        return type.__new__(cls, class_name, class_bases, update_attrs)


class Chinese(metaclass=MyMeta):
    country = 'China'
    tag = 'Legend of the Dragon'

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

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


ch = Chinese('alice')
print(Chinese.__dict__)
'''
{'__module__': '__main__', 'COUNTRY': 'China', 'TAG': 'Legend of the Dragon', 
'__init__': <function Chinese.__init__ at 0x00000235649C0B70>, 
'talk': <function Chinese.talk at 0x00000235649C0BF8>, 
'__dict__': <attribute '__dict__' of 'Chinese' objects>, 
'__weakref__': <attribute '__weakref__' of 'Chinese' objects>, '__doc__': None}

'''

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 Mymeta(type):
    def __call__(self, *args, **kwargs):
        if args:
            raise TypeError('must use keyword argument')
        obj = object.__new__(self)
        for i in kwargs:
            obj.__dict__[i.upper()] = kwargs[i]
        return obj


class Chinese(metaclass=Mymeta):
    country = 'China'
    tag = 'Lengend of the Dragon'
    def talk(self):
        print('%s is talking' % self.NAME)


ch = Chinese(name='alice', age=12)
print(ch.__dict__)
ch.talk()
'''
{'NAME': 'alice', 'AGE': 12}
alice is talking
'''