描述符 

 1 class Type:
 2     def __init__(self,key):
 3         self.key = key
 4 
 5     def __get__(self, instance, owner):
 6         print('执行get方法')
 7         return instance.__dict__[self.key]
 8 
 9     def __set__(self, instance, value):
10         print('执行set方法')
11         instance.__dict__[self.key] = value
12 
13     def __delete__(self, instance):
14         instance.__dict__.pop(self.key)
15 class Foo:
16     name = Type('name')
17 
18     def __init__(self, name):
19         self.name = name
20 
21 
22 f1 = Foo('alex')
23 f1.name = 2
24 print(f1.__dict__)
25 print(f1.name)
26 输出：
27 执行set方法
28 执行set方法
29 {'name': 2}
30 执行get方法
31 2

可以对赋值加上条件判断

 1 class Type:
 2     def __init__(self,key):
 3         self.key = key
 4 
 5     def __get__(self, instance, owner):
 6         print('执行get方法')
 7         return instance.__dict__[self.key]
 8 
 9     def __set__(self, instance, value):
10         print('执行set方法')
11         if not isinstance(value,str):
12             # print('你传入得不是字符串')
13             raise TypeError('你传入的不是字符串')
14         instance.__dict__[self.key] = value
15 
16     def __delete__(self, instance):
17         instance.__dict__.pop(self.key)
18 class Foo:
19     name = Type('name')
20 
21     def __init__(self, name):
22         self.name = name
23 
24 
25 f1 = Foo(3)
26 # f1.name = 2
27 # print(f1.__dict__)
28 # print(f1.name)
29 输出：
30 执行set方法
31 Traceback (most recent call last):
32   File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 25, in <module>
33     f1 = Foo(3)
34   File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 22, in __init__
35     self.name = name
36   File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 13, in __set__
37     raise TypeError('你传入的不是字符串')
38 TypeError: 你传入的不是字符串

 

posted @ 2020-03-13 10:44  竹石2020  阅读(181)  评论(0)  编辑  收藏  举报