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()