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。

>>> shelve.open('1')['b']
[1,2,3]
>>> shelve.close()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
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？

>>> b
[1, 2, 3]
>>> c = shelve.open('5') 
>>> c['b'] = b
>>> c['b']
[1, 2, 3]　　#创建并打开文件5
>>> d = shelve.open('6')
>>> d['b'] = [4,5,6]
>>> d['b']
[4, 5, 6]　　#创建并打开文件6
>>> b
[1, 2, 3]
>>> c['b']
[1, 2, 3]
>>> d.close()
>>> d['b']　　#关闭文件
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
>>> c['b']
[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。

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

shelf值默认返回值为keys()方法的返回值。