Python Common Modules 2

Python Common module Two

Shelve
Pickle
Json

Shelve module

• The internal structure is actually the dictionary type, the storage time specifies the corresponding key, the content is stored as value, and takes out the value directly through key.

• Note that the file name does not require any suffixes because the system defaults to. db as the suffix name.

• Code 1 storing content

import shelvedef fun1():    pass= shelve.open(‘test_shelve‘)s[‘dic‘= {}.fromkeys(list(‘abcdefg‘0)s[‘func‘= fun1s[‘list‘=list(range(10))s.close()

• Code 2 removing content

= shelve.open(‘test_shelve‘= shelve.open(‘test_shelve‘= s.get(‘dic‘= s.get(‘func‘= s.get(‘list‘)

Pickle Module

• Writes and reads are read as bytes, and encoding and decoding formats can be specified

• Write file

import=open(‘save.pkl‘‘wb‘, encoding=‘utf8‘= {}.fromkeys(list(‘qwertasd‘1)pickle.dump(dic, f)f.close()

• Read file

import=open(‘save.pkl‘‘rb‘= pickle.load(f)printtype(data))

JSON module

• Modules include the following functions:

  • The JSON module provides four functions: dumps, dump, loads, load

  • The Pickle module provides four functions: dumps, dump, loads, load

• Code Listing 1: Storing content in JSON serialized format file

= [‘我‘‘你‘‘它‘‘asdas‘=open(‘save.json‘‘w‘)json.dump(s, f)f.close()

• Code Listing 2: Using JSON modules to read JSON-formatted content

=open(‘save.json‘‘r‘, encoding=‘utf8‘= json.load(f1)# result = json.loads(f1.read())

• Serializes the string JSON into a file that is encoded in Unicode format

= json.dumps(s)printtype(data))# ["\u6211", "\u4f60", "\u5b83"] <class ‘str‘>=# 直接反序列json序列化数据print(result)# [‘我‘, ‘你‘, ‘它‘]

JSON, Pickle, shelve three differences

The main differences are several points:

1. The pickle and shelve modules support all Python data types, including functions, but JSON only supports data types such as Dic/list/tuple/str/int;
2. Pikle and shelve can only be used in Python, but JSON is cross-lingual;

The role of JSON, Pickle, shelve three modules

• For converting between strings and python or other programming language data types, not only can you save data to your hard disk, but you can also save its data type

Python Common Modules 2