Python JSON

JSON (JavaScript Object Notation) is a popular data format used for representing structured data. It's common to transmit and receive data between a server and web application in JSON format.

In Python, JSON exists as a string. For example:

p = '{"name": "Bob", "languages": ["Python", "Java"]}'

It's also common to store a JSON object in a file.

Import json Module

To work with JSON (string, or file containing JSON object), you can use Python's json module. You need to import the module before you can use it.

import json

Parse JSON in Python

The json module makes it easy to parse JSON strings and files containing JSON object.

Example 1: Python JSON to dict

You can parse a JSON string using json.loads() method. The method returns a dictionary.

import json

person = '{"name": "Bob", "languages": ["English", "French"]}'
person_dict = json.loads(person)

# Output: {'name': 'Bob', 'languages': ['English', 'French']}
print( person_dict)

# Output: ['English', 'French']
print(person_dict['languages'])

Here, person is a JSON string, and person_dict is a dictionary.

Example 2: Python read JSON file

You can use json.load() method to read a file containing JSON object.

Suppose, you have a file named person.json which contains a JSON object.

{"name": "Bob", 
"languages": ["English", "French"]
}

Here's how you can parse this file:

import json

with open('path_to_file/person.json', 'r') as f:
  data = json.load(f)

# Output: {'name': 'Bob', 'languages': ['English', 'French']}
print(data)

Here, we have used the open() function to read the json file. Then, the file is parsed using json.load() method which gives us a dictionary named data.

If you do not know how to read and write files in Python, we recommend you to check Python File I/O.

Python Convert to JSON string

You can convert a dictionary to JSON string using json.dumps() method.

Example 3: Convert dict to JSON

import json

person_dict = {'name': 'Bob',
'age': 12,
'children': None
}
person_json = json.dumps(person_dict)

# Output: {"name": "Bob", "age": 12, "children": null}
print(person_json)

Here's a table showing Python objects and their equivalent conversion to JSON.

Writing JSON to a file

To write JSON to a file in Python, we can use json.dump() method.

Example 4: Writing JSON to a file

import json

person_dict = {"name": "Bob",
"languages": ["English", "French"],
"married": True,
"age": 32
}

with open('person.txt', 'w') as json_file:
  json.dump(person_dict, json_file)

In the above program, we have opened a file named person.txt in writing mode using 'w'. If the file doesn't already exist, it will be created. Then, json.dump() transforms person_dict to a JSON string which will be saved in the person.txt file.

When you run the program, the person.txt file will be created. The file has following text inside it.

{"name": "Bob", "languages": ["English", "French"], "married": true, "age": 32}

Python pretty print JSON

To analyze and debug JSON data, we may need to print it in a more readable format. This can be done by passing additional parameters indent and sort_keys to json.dumps() and json.dump() method.

Example 5: Python pretty print JSON

import json

person_string = '{"name": "Bob", "languages": "English", "numbers": [2, 1.6, null]}'

# Getting dictionary
person_dict = json.loads(person_string)

# Pretty Printing JSON string back
print(json.dumps(person_dict, indent = 4, sort_keys=True))

When you run the program, the output will be:

{
    "languages": "English",
    "name": "Bob",
    "numbers": [
        2,
        1.6,
        null
    ]
}

In the above program, we have used 4 spaces for indentation. And, the keys are sorted in ascending order.

By the way, the default value of indent is None. And, the default value of sort_keys is False.

Recommended Readings:

• Python JSON to CSV and vice-versa
• Python XML to JSON and vice-versa
• Python simplejson