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实例存储之shelve

2022-08-08 09:32:00 【51CTO】

对于传统的数据库，大家都很清楚是拿来存储数字，字符串，json等等，但是有一点这一类的数据是静态的。如果想保存动态数据，比如对象的实例，有没有可能呢。答案是肯定的。

shelve模块就提供了这种可能性，它是基于pickle模块，是数据持久化的解决方案。

installation

shelve是python内置模块，无需额外安装。

保存实例到文件

       
       import 
       
       shelve
       
       db_name 
       
       = 
       
       'test.db'
       
       class 
       
       Session(
       
       object):
       
       def 
       
       __init__(
       
       self, 
       
       user, 
       
       password):
       
       self.
       
       user 
       
       = 
       
       user
       
       self.
       
       password 
       
       = 
       
       password
       
       def 
       
       run(
       
       self, 
       
       command):
       
       print(
       
       'executing command: {}'.
       
       format(
       
       command))
       
       class 
       
       Host(
       
       object):
       
       def 
       
       __init__(
       
       self, 
       
       user, 
       
       password, 
       
       times):
       
       self.
       
       user 
       
       = 
       
       user
       
       self.
       
       password 
       
       = 
       
       password
       
       self.
       
       times 
       
       = 
       
       times
       
       self.
       
       child 
       
       = 
       
       Session(
       
       user, 
       
       password)
       
       def 
       
       perform(
       
       self):
       
       print(
       
       'user: {}'.
       
       format(
       
       self.
       
       user))
       
       print(
       
       'password: {}'.
       
       format(
       
       self.
       
       password))
       
       for 
       
       i 
       
       in 
       
       range(
       
       1, 
       
       self.
       
       times
       
       +
       
       1):
       
       self.
       
       child.
       
       run(
       
       'hello command {}'.
       
       format(
       
       i))
       
       s 
       
       = 
       
       shelve.
       
       open(
       
       db_name)
       
       s[
       
       'host'] 
       
       = 
       
       Host(
       
       'rock', 
       
       '123456', 
       
       10)
       
       s.
       
       close()
       
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从文件中读取实例

       
       import 
       
       shelve
       
       from 
       
       shelve_test01 
       
       import 
       
       Session, 
       
       Host
       
       db_name 
       
       = 
       
       'test.db'
       
       s 
       
       = 
       
       shelve.
       
       open(
       
       db_name)
       
       host 
       
       = 
       
       s[
       
       'host']
       
       host.
       
       perform()
       
       print(
       
       host.
       
       child.
       
       user)
      
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       user: 
       
       rock
       
       password: 
       
       123456
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       1
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       2
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       3
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       4
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       5
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       6
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       7
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       8
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       9
       
       executing 
       
       command: 
       
       hello 
       
       command 
       
       10
       
       rock
      
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