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

 #encoding=utf-8
 __author__ = 'heng'
 #简单的数据库应用程序

 import sys, shelve

 def store_person(db):
     """
     Query user for data and store it in the shelf object
     """
     pid = raw_input('Enter unique ID number: ')
     person = {}
     person['name'] = raw_input('Enter name: ')
     person['age'] = raw_input('Enter age: ')
     person['phone'] = raw_input('Enter phone number: ')
     db[pid] = person

 def lookup_person(db):
     """
     Query user for ID and desired field, and fetch the corresponding data from
     the shelf object
     """
     pid = raw_input('Enter ID number: ')
     field = raw_input('What would you like to know? (name, age, phone) ')
     field = field.strip().lower()
     print field.capitalize() + ':', \
         db[pid][field]

 def print_help():
     print 'The available commons are: '
     print 'store  :Stores information about a person'
     print 'lookup :Looks up a person from ID number'
     print 'quit   :Save changes and exit'
     print '?      :Print this message'

 def enter_command():
     cmd = raw_input('Enter command (? for help): ')
     cmd = cmd.strip().lower()
     return cmd

 def main():
     database = shelve.open('testdata.dat')
     try:
         while True:
             cmd = enter_command()
             if cmd == 'store':
                 store_person(database)
             elif cmd == 'lookup':
                 lookup_person(database)
             elif cmd == '?':
                 print_help()
             elif cmd == 'quit':
                 return
     finally:
         database.close()
 if __name__ == '__main__': main()