7.4 JSON Files

JSON, short for JavaScript Object Notation, is a common data format. It is often used for configuration files, API responses, and simple data exchange. For Python beginners, JSON is approachable because it resembles dictionaries and lists.

JSON and Python Data

Here is a configuration file named settings.json:

{
  "language": "en",
  "theme": "light",
  "auto_save": true,
  "font_size": 16
}

After Python reads it, it becomes a dictionary:

import json

with open("settings.json", "r", encoding="UTF-8") as file:
    settings = json.load(file)

print(settings["language"])
print(settings["font_size"])

json.load(file) reads JSON from a file object and converts it into Python data.

Writing JSON

Use json.dump() to write a Python dictionary back to a JSON file.

import json

settings = {
    "language": "en",
    "theme": "dark",
    "auto_save": True,
    "font_size": 18
}

with open("settings.json", "w", encoding="UTF-8") as file:
    json.dump(settings, file, ensure_ascii=False, indent=2)

ensure_ascii=False keeps non-English text readable, and indent=2 makes the JSON easier to inspect.