shelve模块读写文件报错

import shelve

a = shelve.open('1')
b = [1,2,3]
a['b'] = b
a.close()

a['b']

Traceback (most recent call last):
File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 111, in __getitem__
value = self.cache[key]
KeyError: 'b'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 113, in __getitem__
f = BytesIO(self.dict[key.encode(self.keyencoding)])
File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 70, in closed
raise ValueError('invalid operation on closed shelf')
ValueError: invalid operation on closed shelf

原因是a.close()就已经关闭了shelf文件。

1 >>> shelve.open('1')['b']
2 [1,2,3]
3 >>> shelve.close()
4 Traceback (most recent call last):
5   File "<stdin>", line 1, in <module>
6 AttributeError: module 'shelve' has no attribute 'close'

shelve模块没有close()，需要变量来关闭。

那如果没有关闭会怎样？

 1 >>> b
 2 [1, 2, 3]
 3 >>> c = shelve.open('5') 
 4 >>> c['b'] = b
 5 >>> c['b']
 6 [1, 2, 3]　　#创建并打开文件5
 7 >>> d = shelve.open('6')
 8 >>> d['b'] = [4,5,6]
 9 >>> d['b']
10 [4, 5, 6]　　#创建并打开文件6
11 >>> b
12 [1, 2, 3]
13 >>> c['b']
14 [1, 2, 3]
15 >>> d.close()
16 >>> d['b']　　#关闭文件
17 Traceback (most recent call last):
18   File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 111, in __getitem__
19     value = self.cache[key]
20 KeyError: 'b'
21 
22 During handling of the above exception, another exception occurred:
23 
24 Traceback (most recent call last):
25   File "<stdin>", line 1, in <module>
26   File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 113, in __getitem__
27     f = BytesIO(self.dict[key.encode(self.keyencoding)])
28   File "C:UsersAdministratorAppDataLocalProgramsPythonPython38-32libshelve.py", line 70, in closed
29     raise ValueError('invalid operation on closed shelf')
30 ValueError: invalid operation on closed shelf
31 >>> c['b']
32 [1, 2, 3]

从上面代码可以看出shelve模块的close()是分别针对每个文件的，会一直处于打开状态直到关闭。

1 >>> list(c.values())
2 [[1, 2, 3]]
3 >>> list(c.keys())
4 ['b']
5 >>> list(c)
6 ['b']

shelf值默认返回值为keys()方法的返回值。