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

 1 class MyMeta(type):
 2     def __new__(cls, class_name, class_bases, class_dic):
 3         update_attrs = {}
 4         for i in class_dic:
 5             if not callable(class_dic[i]) and not i.startswith('__'):
 6                 update_attrs[i.upper()] = class_dic[i]
 7             else:
 8                 update_attrs[i] = class_dic[i]
 9         return type.__new__(cls, class_name, class_bases, update_attrs)
10 
11 
12 class Chinese(metaclass=MyMeta):
13     country = 'China'
14     tag = 'Legend of the Dragon'
15 
16     def __init__(self, name):
17         self.name = name
18 
19     def talk(self):
20         print('%s is talking' % self.name)
21 
22 
23 ch = Chinese('alice')
24 print(Chinese.__dict__)
25 '''
26 {'__module__': '__main__', 'COUNTRY': 'China', 'TAG': 'Legend of the Dragon', 
27 '__init__': <function Chinese.__init__ at 0x00000235649C0B70>, 
28 'talk': <function Chinese.talk at 0x00000235649C0BF8>, 
29 '__dict__': <attribute '__dict__' of 'Chinese' objects>, 
30 '__weakref__': <attribute '__weakref__' of 'Chinese' objects>, '__doc__': None}
31 
32 '''


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

 1 class Mymeta(type):
 2     def __call__(self, *args, **kwargs):
 3         if args:
 4             raise TypeError('must use keyword argument')
 5         obj = object.__new__(self)
 6         for i in kwargs:
 7             obj.__dict__[i.upper()] = kwargs[i]
 8         return obj
 9 
10 
11 class Chinese(metaclass=Mymeta):
12     country = 'China'
13     tag = 'Lengend of the Dragon'
14     def talk(self):
15         print('%s is talking' % self.NAME)
16 
17 
18 ch = Chinese(name='alice', age=12)
19 print(ch.__dict__)
20 ch.talk()
21 '''
22 {'NAME': 'alice', 'AGE': 12}
23 alice is talking
24 '''