Files, Errors and Modules · Working at Scale · lesson 7 of 8

JSON in and out

about 14 minutes · free · runs in your browser

Step 1 of 2

Text in, objects out

JSON is how programs exchange structured data. The json module converts both ways:

import json

text = json.dumps({"name": "Ada", "age": 36})     # object → string
data = json.loads('{"name": "Ada"}')              # string → object

Remember which is which by the s: dumps and loads work with strings, while dump and load work with files.

The mapping is close but not exact. Python's None becomes null, True becomes true, and both tuples and lists come back as lists. Dictionary keys are always strings in JSON, so {1: "a"} returns as {"1": "a"}.

json.dumps(data, indent=2) gives readable output, and sort_keys=True makes it stable — which matters if you ever compare two files.

Malformed text raises json.JSONDecodeError, a subclass of ValueError.

Your turn: write parse_config(text) returning the parsed dictionary, or an empty dictionary when the text is not valid JSON.

You start from this, and edit it in the browser:

import json


def parse_config(text):
    # Parse the JSON, or return {} when it is malformed.
    pass

Step 2 of 2

Writing JSON back out

json.dumps turns Python data into text you can store or send.

Your turn: write to_json(records) returning the list as JSON with keys sorted and no spaces wasted — use separators=(",", ":") for the compact form.

You start from this, and edit it in the browser:

import json


def to_json(records):
    # Return compact JSON with sorted keys.
    pass