Posted on December 19, 2020



JavaScript Object Notation (JSON) is a common data format that is supported natively in Python. The format is built on name/value pairs and ordered list values. Visit json.org to learn more about the JSON format.

Load a JSON file

The contents of a JSON file named books.json are shown below:

        "title": "Alice's Adventures in Wonderland",
        "author": "Lewis Carroll",
        "year": 1865
        "title": "Do Androids Dream of Electric Sheep",
        "author": "Philip K. Dick",
        "year": 1968
        "title": "The Lorax",
        "author": "Dr. Seuss",
        "year": 1971

To read this file, use the json module to load the contents of the file. The example below prints the title, author, and year for each book item in the JSON file.

import json

with open("books.json") as json_file:
    data = json.load(json_file)

for d in data:
    print(f"{d['title']} by {d['author']} in {d['year']}")

This prints the following:

Alice's Adventures in Wonderland by Lewis Carroll in 1865
Do Androids Dream of Electric Sheep by Philip K. Dick in 1968
The Lorax by Dr. Seuss in 1971

Read a JSON file containing comments

JSON does not support comments. However, commented lines in a JSON file can be ignored when reading the file line-by-line. The function shown below reads a JSON file that contains comments denoted by // and returns the JSON data as a dictionary. An example of using the function is also given.

def read_json(jsonfile, comment='//'):
    json_str = ''

    with open(jsonfile, 'r') as json_file:
        for line in json_file:
            if comment not in line:
                json_str += line

    json_dict = json.loads(json_str)
    return json_dict
>>> file = 'example.json'
>>> jsondict = read_json(file)
>>> jsondict[1]['first_name']


Gavin Wiggins © 2020