【7.5】自定义元类

元类是什么--元类是创建类的类

 1 #!/user/bin/env python
 2 # -*- coding:utf-8 -*-
 3 
 4 # 类也是对象，type创建类的类
 5 
 6 
 7 def create_class(name):
 8     if name == 'user':
 9         class User:
10             def __str__(self):
11                 return 'user'
12         return User
13     elif name == 'company':
14         class Company:
15             def __str__(self):
16                 return 'company'
17         return Company
18 
19 
20 # type动态创建类
21 User = type('User', (), {})
22 
23 
24 def say(self):
25     return 'i am user'
26 
27 
28 class BaseClass:
29     def answer(self):
30         return 'i am baseclass'
31 
32 
33 # 什么是元类， 元类是创建类的类
34 class MetaClass(type):
35     def __new__(cls, *args, **kwargs):
36         return super().__new__(cls, *args, **kwargs)
37 
38 
39 class User(metaclass=MetaClass):
40     def __init__(self, name):
41         self.name = name
42 
43     def __str__(self):
44         return 'user'
45 
46 
47 # python 中类的实例化过程，会首先寻找metaclass， 通过metaclass去创建user类
48 # type去创建类对象，实例
49 
50 
51 if __name__ == '__main__':
52     # MyClass = create_class('user')
53     # my_obj = MyClass()
54     # print(my_obj)
55     User = type('User', (BaseClass,), {'name': 'user', 'say': say})
56     user = User()
57     print(user.name)
58     print(user.say())
59     print(user.answer())

user
i am user
i am baseclass