Python json.dumps - How to write json data to a file in Python

To write data (as a Python list or dictionary) to a json file, the json.dumps() is needed to convert it to the string.

import json

a = [1, 2, 3]
j = json.dumps(a)

with open('a.json', 'w') as f:
    f.write(j)

The a.json contains:

[1, 2, 3]

Example

import json

a = {'r': [1, 2, 3], 'd': {'x': 5, 'y': 7}}
j = json.dumps(a)

with open('a.json', 'w') as f:
    f.write(j)

a.json

{"r": [1, 2, 3], "d": {"x": 5, "y": 7}}

Indent

import json

a = {'r': [1, 2, 3], 'd': {'x': 5, 'y': 7}}
j = json.dumps(a, indent=4)

with open('a.json', 'w') as f:
    f.write(j)

If the indent option of json.dumps() is 4, the data is printed in the json file with 4 indents.

a.json

{
    "r": [
        1,
        2,
        3
    ],
    "d": {
        "x": 5,
        "y": 7
    }
}

Sort keys

import json

a = {'r': [1, 2, 3], 'd': {'x': 5, 'y': 7}}
j = json.dumps(a, indent=4, sort_keys=True)

with open('a.json', 'w') as f:
    f.write(j)

If the sort_keys option of json.dumps() is true, the printed data is sorted by dictionary keys.

a.json

{
    "d": {
        "x": 5,
        "y": 7
    },
    "r": [
        1,
        2,
        3
    ]
}

The dictionary a starts with r key but the printed data starts with d key.