JSON Files — loads, dumps, load, and dump

JSON is a light text format for exchanging data. In Python it lines up with a dict: names and values. The json module converts both ways.

Use the playground at the bottom of this page, then take the quiz.

What you will learn

• Why JSON shows up between programs
• json.loads and json.dumps for a string
• json.load and json.dump for a .json file
• How to walk the dict with m and p

The idea

JSON (JavaScript Object Notation) is language-independent. A Python service and a web client can both read it. The file extension is .json, and the contents look like a dict written as text.

Function	Direction
json.loads(text)	JSON string → dict
json.dumps(record)	dict → JSON string
json.load(handle)	JSON file → dict
json.dump(record, handle)	dict → JSON file

loads and dumps never touch a file. load and dump use a text file pointer. Open that file with "r" or "w". A missing file raises FileNotFoundError.

After loads or load, walk the dict with for m, p in record.items(). m is the name. p is the value. JSON objects become dicts. JSON arrays become lists. JSON numbers become int or float, which is different from CSV, where every cell is a string.

dumps is the string form of dump. The teaching notes focus on loads, load, and dump; dumps is the matching way to build the JSON string those notes start from.

The profile below uses a general name and a role. It is not taken from a sample .json file in the notes.

Example

import json

text = '{"label": "Avery Lane", "role": "Guide", "seats": 18}'
record = json.loads(text)
for m, p in record.items():
    print(m, "-->", p)

with open("profile.json", "w", encoding="utf-8") as handle:
    json.dump(record, handle)

with open("profile.json", "r", encoding="utf-8") as handle:
    loaded = json.load(handle)

print(json.dumps(loaded))

seats stays a number because JSON numbers are not quoted. The playground prints each pair and then the dumped string. Change role and run again.

Key takeaways

• JSON text maps to Python dicts and lists

• loads / dumps work on strings

• load / dump work on .json files

• Walk pairs with for m, p in record.items()

• Numbers in JSON stay numbers; CSV cells come back as strings

• Previous: DictWriter and DictReader

• Next: The os Module