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()