Modern Python Standard Library Cookbook

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A few things need attention when working with shelve.

First of all, shelve doesn't track mutations. If you store a mutable object (such as dict or list) in shelf, any change you do to it won't be saved. Only changes to the root keys of shelf itself are tracked:

>>> with shelve.open('/tmp/shelf.db') as shelf:
...   shelf['value'].value = 10
... 
>>> with shelve.open('/tmp/shelf.db') as shelf:
...   print(shelf['value'].value)
... 
5

This just means that you need to reassign any value you want to mutate:

>>> with shelve.open('/tmp/shelf.db') as shelf:
...   myvalue = shelf['value']
...   myvalue.value = 10
...   shelf['value'] = myvalue
... 
>>> with shelve.open('/tmp/shelf.db') as shelf:
...   print(shelf['value'].value)
... 
10

shelve doesn't ...