Introduction to JSON

JSON(JavaScript Object Notation), namely JavaScript object notation, is a lightweight and general text data format.
JSON syntax supports objects, arrays, strings, numbers (int/float), and true/false and null.
JSON has a strict format. The main formats are as follows:

• You can only use double quotation marks, not single quotation marks
• The elements are separated by commas. The last element cannot have commas
• Comments are not supported
• Chinese and other special characters shall be converted to ASCII code (\ uXXX format) during transmission
• Supports multi-layer nested objects or arrays

Sample format, file demo json:

{
    "name": "Cactus",
    "age": 18,
    "skills": ["Python", "Java", "Go", "NodeJS"],
    "has_blog": true,
    "gf": null
}

Correspondence between JSON and Python data types

JSON corresponds to the dictionary and other types in Python one by one:

Note: in Python in, JSON Generally refers to compliance JSON A string in syntax format is actually a string, single line or multiple lines.

Conversion between string and Python dictionary

Why should we convert each other? JSON is a string, which is convenient for storage and transmission and inconvenient for extracting values; Dictionary is a data structure in memory, which is convenient for value taking and inconvenient for transmission and storage

Using Python's own JSON package can complete the conversion between dictionary and JSON string

• json. Dumps: converts a dictionary to a JSON string
• json.loads(JSON string): converts a JSON string into a dictionary. If the string is not in a legal JSON format, JSONDecodeError will be reported

Example 1: dictionary to JSON string

import json

dict_var = {
    'name': 'Cactus', 
    'age': 18, 
    'skills': ['Python', 'Java', 'Go', 'NodeJS'], 
    'has_blog': True, 
    'gf': None
}

print(json.dumps(dict_var))
print(json.dumps(dict_var, indent=2,sort_keys=True, ensure_ascii=False))

json.dumps() supports parameters, indent is the number of indented spaces in multiple lines, sort_keys is whether to sort the keys, ensure_ascii=False means that ascii is not guaranteed, and special characters such as Chinese are not converted to \ uXXX, etc

Display results:

{"name": "Cactus", "age": 18, "skills": ["Python", "Java", "Go", "NodeJS"], "has_blog": true, "gf": null}
{
  "age": 18,
  "gf": null,
  "has_blog": true,
  "name": "Cactus",
  "skills": [
    "Python",
    "Java",
    "Go",
    "NodeJS"
  ]
}

Example 2: JSON string - > dictionary

import json

json_str = '''{
    "name": "Cactus",
    "age": 18,
    "skills": ["Python", "Java", "Go", "NodeJS"],
    "has_blog": true,
    "gf": null
}'''

print(json.loads(json_str))

Display results:

{'name': 'Cactus', 'age': 18, 'skills': ['Python', 'Java', 'Go', 'NodeJS'], 'has_blog': True, 'gf': None}

Conversion between JSON file and dictionary

In addition, you can directly save the dictionary as a JSON file or convert it from a JSON file to a dictionary

• json. Dump (Dictionary, f): convert dictionary to JSON file (handle)
• json.loads(f): turns the handle of the open JSON file into a dictionary

Example 3: Dictionary - > JSON file

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'''
import json

dict_var = {
    'name': 'Cactus', 
    'age': 18, 
    'skills': ['Python', 'Java', 'Go', 'NodeJS'], 
    'has_blog': True, 
    'gf': None
}

with open("demo2.json", "w", encoding='utf-8') as f:
    # json.dump(dict_var, f)  # Write as one line
    json.dump(dict_var, f,indent=2,sort_keys=True, ensure_ascii=False)  # Write as multiple lines

File demo2 JSON result:

{
  "age": 18,
  "gf": null,
  "has_blog": true,
  "name": "Cactus",
  "skills": [
    "Python",
    "Java",
    "Go",
    "NodeJS"
  ]
}

Example 4: JSON file - > dictionary

import json

with open("demo2.json", encoding="utf-8") as f:
    data = json.load(f)

pritn(data)

Display results:

{'age': 18, 'gf': None, 'has_blog': True, 'name': 'Cactus', 'skills': ['Python', 'Java', 'Go', 'NodeJS']}

Note: when the dictionary is converted to JSON, only nested dictionaries, lists, strings, numbers, True/False/None, etc. are supported, and date objects and other Python objects are not supported

To resolve complex nested JSON format, please use JSONPath