举例简单讲解Python中的数据存储模块shelve的用法

import shelve


def test_shelve():
 # open 返回一个Shelf类的实例
 #
 # 参数flag的取值范围：
 # 'r'：只读打开
 # 'w'：读写访问
 # 'c'：读写访问，如果不存在则创建
 # 'n'：读写访问，总是创建新的、空的数据库文件
 #
 # protocol：与pickle库一致
 # writeback：为True时，当数据发生变化会回写，不过会导致内存开销比较大
 d = shelve.open('shelve.db', flag='c', protocol=2, writeback=False)
 assert isinstance(d, shelve.Shelf)

 # 在数据库中插入一条记录
 d['abc'] = {'name': ['a', 'b']}
 d.sync()

 print d['abc']

 # writeback是False，因此对value进行修改是不起作用的
 d['abc']['x'] = 'x'
 print d['abc'] # 还是打印 {'name': ['a', 'b']}

 # 当然，直接替换key的value还是起作用的
 d['abc'] = 'xxx'
 print d['abc']

 # 还原abc的内容，为下面的测试代码做准备
 d['abc'] = {'name': ['a', 'b']}
 d.close()

 # writeback 为 True 时，对字段内容的修改会writeback到数据库中。
 d = shelve.open('shelve.db', writeback=True)

 # 上面我们已经保存了abc的内容为{'name': ['a', 'b']}，打印一下看看对不对
 print d['abc']

 # 修改abc的value的部分内容
 d['abc']['xx'] = 'xxx'
 print d['abc']
 d.close()

 # 重新打开数据库，看看abc的内容是否正确writeback
 d = shelve.open('shelve.db')
 print d['abc']
 d.close()

>>> import shelve 
>>> s = shelve.open('test.dat') 
>>> s['x'] = ['a', 'b', 'c'] 
>>> s['x'].append('d') 
>>> s['x'] 
['a', 'b', 'c'] 

>>> temp = s['x'] 
>>> temp.append('d') 
>>> s['x'] = temp 
>>> s['x'] 
['a', 'b', 'c', 'd'] 

#database.py 
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('database.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()