A brief introduction to the shelve module in Python (with examples)-Python Tutorial-php.cn

A brief introduction to the shelve module in Python (with examples)

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Release： 2018-09-25 17:15:39

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This article brings you a brief introduction to the shelve module in Python (with examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

shelve: A module for object persistence that saves objects to files (the default data storage file is binary) and can persist any Python data format supported by pickle

The only method in shelve:

shelve.open(filename,flag = 'c', protocol = None, writebake = False)

filename	Associated file path
flag	'r' : Open an existing data storage file in read-only mode
	' w' : Open an existing data storage file in read-write mode
	'c' : (Default) Open an existing data storage file in read-write mode, Create if not present
	'n' : Always open in read-write mode and create a new empty data storage file
protocol	indicates the protocol used to serialize data, the default is None (pickle v3)
writebake	Indicates whether to enable the writeback function

##1. The file can store key - value like a dictionary (Note: key must be a string, value can be any data type)

import shelve
date = shelve.open(&#39;family.txt&#39;)         # Python的自处理系统会自动生成三个文件
date[&#39;father&#39;] = &#39;Presly&#39;                        # 默认为创建并且写入“c”
date[&#39;mather&#39;] = &#39;Vera&#39;
date[&#39;baby&#39;] = [123, ]
date.close()
m = shelve.open(&#39;family.txt&#39;, falg= &#39;r&#39;, writebake=True)          # 当writebake设置为True时，文件里才能直接添加
print(m[&#39;baby&#39;]) 
m[&#39;baby&#39;].append(345)
print(m[&#39;father&#39;])
print(&#39;-------------&#39;) 
for key, value in m.items():           # 以字典的格式 
    print(key, &#39;:&#39;, value) 
m.close()

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[123]
Presly
-------------
father : Presly
mather : Vera
baby : [123，345]

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2. Serialization of shelve

#You can serialize the class data and then deserialize the elements
Different from pickle, pickle can only load elements in the dump order, while shelve can directly repeatedly take out different or the same key values that are stored in the file,

3. shelve can perform operations similar to libraries, add, delete, modify, and check

import shelve


def store_information(database):
    info = {}
    ID = input(&#39;Enter the ID number:&#39;)
    info[&#39;name&#39;] = input(&#39;Enter the name:&#39;)         # 将name ,age , phone 存入字典info里
    info[&#39;age&#39;] = input(&#39;Enter the age:&#39;)
    info[&#39;phone&#39;] = input(&#39;Enter the phone:&#39;)
    database[ID] = info                            # 用ID ： info 存入 database文件


def lookup_information(database):
    ID = input(&#39;Enter the ID:&#39;)
    field = input(&#39;What would you like to know?(name,age,phone)&#39;)
    field = field.strip().lower()
    print(database[ID][field])              # 通过输入的ID与 field 直接打印结果


def print_help():
    print(&#39;Please enter the help command:&#39;)
    print(&#39;store  :store informatinon to database&#39;)
    print(&#39;lookup :look up information by numID&#39;)
    print(&#39;quit   :save information and quit&#39;)
    print(&#39;?      :print help command&#39;)


def enter_command():
    cmd = input(&#39;Enter command (? for help)&#39;)
    cmd = cmd.strip().lower()
    return cmd


def main():
    database = shelve.open(&#39;db.dat&#39;)
    try:
        while True:
            cmd = enter_command()
            if cmd == &#39;store&#39;:
                store_information(database)           # 当if函数结束，自动跳转到cmd = enter_command()行
            elif cmd == &#39;lookup&#39;:
                lookup_information(database)
            elif cmd == &#39;?&#39;:
                print_help()
            elif cmd == &#39;quit&#39;:
                return                            # 跳出while循环
    finally:
        database.close()


if __name__ == &#39;__main__&#39;: main()

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