第 46 讲 魔法方法 描述符（Property的原理）

黄金猫

1. 课堂笔记:
   
2.   1. 文件打开用with open(path) as f 不用f.close(),方便
   
3. 
   
4. 测试题:
   
5. 0.
   
6. 描述符是一个至少有__get__(self,instance,owner),__set__(self,instance,value),__delete__(self,instance)其一的类,并把这个类的实例对象赋予其他类的属性,被赋予属性的类就被描述符描述了.
   
7. 
   
8. 一个程序有一个需求,在变量被查找赋值或删除时执行,就用描述符来完成.
   
9. 
   
10. 1.
    
11. get:__get__(self,instance,owner),
    
12. set:__set__(self,instance,value),
    
13. del:__delete__(self,instance)
    
14. 
    
15. 2.
    
16. 都会
    
17. 
    
18. 3.
    
19. 20
    
20. 0
    
21. 
    
22. 4.
    
23. 9
    
24. 返回实例层次的描述符,会返回描述符本身,必须调用类层次的描述符,否则无法调用set,get等方法.
    
25. 
    
26. 
    
27. 动动手:
    
28. 0.
    
29. class MyDes:
    
30.     def __init__(self,value = 0,name = '未命名'):
    
31.         self.value = value
    
32.         self.name = name
    
33. 
    
34.     def __get__(self,instance,owner):
    
35.         print('正在获取变量:',self.name)
    
36.         return self.value
    
37. 
    
38.     def __set__(self,instance,value):
    
39.         print('正在修改变量:',self.name)
    
40.         self.value = value
    
41. 
    
42.     def __delete__(self,instance):
    
43.         print('正在删除变量:',self.name)
    
44.         print('噢,这个变量没法删除~')
    
45. 
    
46. class Test:
    
47.     x = MyDes(10,'x')
    
48. 
    
49. test = Test()
    
50. 
    
51. 1.
    
52. i         self.name = name
    
53. 
    
54.     def __get__(self,instance,owner):
    
55.         print('%s 变量于北京时间 %s 被读取,%s = ' % (self.name,t.asctime(),self.name),self.value)
    
56.         get_record = '%s 变量于北京时间 %s 被读取,%s = ' % (self.name,t.asctime(),self.name) + str(self.value) + '\n'
    
57.         f = open('/Users/yufan/Documents/python编程/46/46dds1_record.txt','a',encoding = 'GBK')
    
58.         f.write(get_record)
    
59.         f.close()
    
60.         return self.value
    
61. 
    
62.     def __set__(self,instance,value):
    
63.         self.value = value
    
64.         print('%s 变量于北京时间 %s 被修改,%s = ' % (self.name,t.asctime(),self.name),self.value)
    
65.         set_record = '%s 变量于北京时间 %s 被修改,%s = ' % (self.name,t.asctime(),self.name) + str(self.value) + '\n'
    
66.         f = open('/Users/yufan/Documents/python编程/46/46dds1_record.txt','a',encoding = 'GBK')
    
67.         f.write(set_record)
    
68.         f.close()
    
69.         
    
70. class Test:
    
71.     x = Record(10,'x')
    
72.     y = Record(8.8,'y')
    
73. 
    
74. test = Test()
    
75. 
    
76. 2.
    
77. import pickle as p
    
78. import os
    
79. 
    
80. class MyDes:
    
81.     def __init__(self,name = '未命名',value = 0):
    
82.         self.name = name
    
83.         self.value = value
    
84. 
    
85.     def __get__(self,instance,owner):
    
86.         return self.value
    
87. 
    
88.     def __set__(self,instance,value):
    
89.         self.value = value
    
90.         set_file = open('/Users/yufan/Documents/python编程/46/46dds2/%s.pkl' % self.name,'wb')
    
91.         p.dump(self.value,set_file)
    
92.         set_file.close()
    
93. 
    
94.     def __delete__(self,instance):
    
95.         os.remove('/Users/yufan/Documents/python编程/46/46dds2/%s.pkl' % self.name)
    
96. 
    
97. class Test:
    
98.     x = MyDes('x')
    
99.     y = MyDes('y')
    
100. 
     
101. test = Test()
     

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