Python JSON

What is JSON?

JSON (JavaScript Object Notation) is the most common format for exchanging data between systems — especially web APIs. It looks similar to Python dictionaries and lists. Python's built-in json module converts between Python objects and JSON strings. Key functions: dumps = dict → string, loads = string → dict, dump = write to file, load = read from file. The "s" suffix stands for "string".

Python → JSON with dumps()

Python True/False/None automatically become JSON true/false/null. Use indent=2 for human-readable output.

import json
data = {{"name": "Alice", "age": 28, "skills": ["Python", "SQL"], "active": True}}

print(json.dumps(data))             # compact
print(json.dumps(data, indent=2))   # pretty

{{"name": "Alice", "age": 28, "skills": ["Python", "SQL"], "active": true}}
{{
  "name": "Alice",
  "age": 28,
  "skills": [
    "Python",
    "SQL"
  ],
  "active": true
}}

JSON → Python with loads()

loads() parses a JSON string into Python objects. This is what you use when you get a response from a web API.

import json
js = '{"city": "London", "temp": 12.5, "rain": true}'
w = json.loads(js)
print(type(w))          # dict
print(w["city"])
print(w["rain"])        # JSON true → Python True

London
True

Reading and Writing JSON Files

json.dump() writes to a file; json.load() reads from one. This is the standard way to save configuration or persistent data between program runs.

import json
cfg = {{"theme": "dark", "font": 14}}
with open("config.json", "w") as f:
    json.dump(cfg, f, indent=2)

with open("config.json") as f:
    loaded = json.load(f)
print(loaded["theme"])

dark