shelve — 对象的持久化存储

创建新的Shelf

# shelve_create.py
import shelve

with shelve.open('test_shelf.db') as s:
    s['key1'] = {
        'int': 10,
        'float': 9.5,
        'string': 'Sample data',
    }

# shelve_existing.py
import shelve

with shelve.open('test_shelf.db') as s:
    existing = s['key1']

print(existing)

# shelve_readonly.py
import dbm
import shelve

with shelve.open('test_shelf.db', flag='r') as s:
    print('Existing:', s['key1'])
    try:
        s['key1'] = 'new value'
    except dbm.error as err:
        print('ERROR: {}'.format(err))

回写

# shelve_withoutwriteback.py
import shelve

with shelve.open('test_shelf.db') as s:
    print(s['key1'])
    s['key1']['new_value'] = 'this was not here before'

with shelve.open('test_shelf.db', writeback=True) as s:
    print(s['key1'])

# shelve_writeback.py
import shelve
import pprint

with shelve.open('test_shelf.db', writeback=True) as s:
    print('Initial data:')
    pprint.pprint(s['key1'])

    s['key1']['new_value'] = 'this was not here before'
    print('\nModified:')
    pprint.pprint(s['key1'])

with shelve.open('test_shelf.db', writeback=True) as s:
    print('\nPreserved:')
    pprint.pprint(s['key1'])