Python中的shelve模块

shelve中有用的函数就是open(),但是下面编写的数据库函数中调用路径是经常出错，如果直接调用一个从来没有用过的文件却能正常运行，暂时没有找出原因。

调用shelve.open()会返回一个shelf对象用来存储内容，将它当做一个普通的字典来存储数据（字典的键一定要是字符串），在存储完毕之后要调用close()函数，关闭文件。

注意为了正确的使用shelve模块修改存储的对象，必须将临时变量绑定到获得的副本上，并且在修改后重新存储这个副本。或者直接将open()中writeback参数设为True。

下面是利用shelve模块建立的小型数据库

 1 #encoding=utf-8
 2 __author__ = ‘heng‘
 3 #简单的数据库应用程序
 4
 5 import sys, shelve
 6
 7 def store_person(db):
 8     """
 9     Query user for data and store it in the shelf object
10     """
11     pid = raw_input(‘Enter unique ID number: ‘)
12     person = {}
13     person[‘name‘] = raw_input(‘Enter name: ‘)
14     person[‘age‘] = raw_input(‘Enter age: ‘)
15     person[‘phone‘] = raw_input(‘Enter phone number: ‘)
16     db[pid] = person
17
18 def lookup_person(db):
19     """
20     Query user for ID and desired field, and fetch the corresponding data from
21     the shelf object
22     """
23     pid = raw_input(‘Enter ID number: ‘)
24     field = raw_input(‘What would you like to know? (name, age, phone) ‘)
25     field = field.strip().lower()
26     print field.capitalize() + ‘:‘, 27         db[pid][field]
28
29 def print_help():
30     print ‘The available commons are: ‘
31     print ‘store  :Stores information about a person‘
32     print ‘lookup :Looks up a person from ID number‘
33     print ‘quit   :Save changes and exit‘
34     print ‘?      :Print this message‘
35
36 def enter_command():
37     cmd = raw_input(‘Enter command (? for help): ‘)
38     cmd = cmd.strip().lower()
39     return cmd
40
41 def main():
42     database = shelve.open(‘testdata.dat‘)
43     try:
44         while True:
45             cmd = enter_command()
46             if cmd == ‘store‘:
47                 store_person(database)
48             elif cmd == ‘lookup‘:
49                 lookup_person(database)
50             elif cmd == ‘?‘:
51                 print_help()
52             elif cmd == ‘quit‘:
53                 return
54     finally:
55         database.close()
56 if __name__ == ‘__main__‘: main()