Python JSON

Python JSON: Parsing and Serializing Data with the json Module

Python's built-in json module converts between JSON text and Python dictionaries, lists, strings, numbers, booleans, and None. Every REST API integration, webhook handler, and configuration loader uses json to read and write structured payloads.

JSON keys must always be double-quoted strings, and trailing commas are invalid. Python handles these format rules automatically when you serialize with json.dumps().

Converting Between Python and JSON Strings

Use json.loads() ("load string") to parse JSON text into Python data, and json.dumps() ("dump string") to serialize Python data back into JSON text.

import json

payload = '{"user": "lina", "active": true, "roles": ["editor", "viewer"]}'
data = json.loads(payload)
print(data["user"], data["roles"][0])

output = json.dumps({"status": "ok", "count": 2}, indent=2)
print(output)

Reading and Writing JSON Files

For files on disk, use json.load(file) and json.dump(data, file) inside a with open(...) block using UTF-8 encoding.

from pathlib import Path
import json

config = {"theme": "dark", "retries": 3}
Path("settings.json").write_text(json.dumps(config, indent=2), encoding="utf-8")

Common Mistakes to Avoid

• Confusing load/loads and dump/dumps: The trailing s stands for string; json.load() expects a file object, while json.loads() expects a str.
• Serializing Python set or datetime directly: JSON only supports dicts, lists, strings, numbers, booleans, and null; convert sets to lists and dates to .isoformat().
• Using eval() to parse JSON: Never pass untrusted text to eval(); json.loads() is safe and rejects non-JSON syntax like single quotes.

Frequently Asked Questions

How do Python types map to JSON types?

Python dict becomes a JSON object, list and tuple become JSON arrays, True/False become true/false, and None becomes null.

How do I handle invalid JSON without crashing?

Wrap json.loads(raw_text) in try ... except json.JSONDecodeError as err: to log or return a clean validation error.

Why do integer dictionary keys turn into strings in JSON?

JSON object keys must be strings, so json.dumps({1: "a"}) produces '{"1": "a"}', and parsing it back yields string keys.