Working with JSON in Python

JSON (JavaScript Object Notation) is a lightweight data format commonly used for data exchange between systems. Python provides the json module to parse JSON data and convert Python objects to JSON.

Importing the json Module

import json

JSON Basics

Example JSON String

{
  "name": "Alice",
  "age": 25,
  "skills": ["Python", "Data Analysis", "Machine Learning"],
  "is_student": false
}

JSON vs. Python

JSON Data Type Python Data Type
Object Dictionary
Array List
String String
Number int or float
Boolean bool
null None

Reading JSON

Parse JSON String to Python Object

json_string = '{"name": "Alice", "age": 25, "is_student": false}'
data = json.loads(json_string)

print(data)         # Output: {'name': 'Alice', 'age': 25, 'is_student': False}
print(data['name']) # Output: Alice

Writing JSON

Convert Python Object to JSON String

python_data = {
    "name": "Alice",
    "age": 25,
    "skills": ["Python", "Data Analysis"],
    "is_student": False
}

json_string = json.dumps(python_data)
print(json_string)

Indented and Sorted JSON

json_string = json.dumps(python_data, indent=4, sort_keys=True)
print(json_string)

Working with Files

Reading JSON from a File

with open("data.json", "r") as file:
    data = json.load(file)

print(data)

Writing JSON to a File

with open("data.json", "w") as file:
    json.dump(python_data, file, indent=4)

Handling Errors

Invalid JSON

try:
    invalid_json = '{"name": "Alice", "age": 25,}'
    data = json.loads(invalid_json)
except json.JSONDecodeError as e:
    print("Invalid JSON:", e)

Advanced Usage

Custom Serialization

Python objects that are not directly serializable (e.g., datetime) can be handled using a custom serializer.

Serializing datetime

from datetime import datetime

data = {"event": "Launch", "date": datetime.now()}

def custom_serializer(obj):
    if isinstance(obj, datetime):
        return obj.isoformat()
    raise TypeError("Type not serializable")

json_string = json.dumps(data, default=custom_serializer)
print(json_string)

Deserializing datetime

def custom_deserializer(dct):
    if "date" in dct:
        dct["date"] = datetime.fromisoformat(dct["date"])
    return dct

json_string = '{"event": "Launch", "date": "2025-01-16T10:30:00"}'
data = json.loads(json_string, object_hook=custom_deserializer)
print(data)

Practical Examples

API Response Simulation

response = '{"status": "success", "data": {"id": 123, "name": "Alice"}}'
data = json.loads(response)
print(data["data"]["name"])  # Output: Alice

Configuration File

config = {
    "theme": "dark",
    "language": "en",
    "autosave": True
}

with open("config.json", "w") as file:
    json.dump(config, file, indent=4)

# Reading the configuration
with open("config.json", "r") as file:
    config = json.load(file)
    print(config["theme"])  # Output: dark

Best Practices

  1. Validate JSON Data:
    • Use try-except to handle potential parsing errors.
  2. Use Indentation:
    • Add indent=4 when writing JSON to improve readability.
  3. Serialize Non-Standard Objects:
    • Provide a default function to handle custom objects.

Practice Exercises

  1. JSON Parsing:
    • Write a script to parse a JSON string representing a list of users and print their names.
  2. File Handling:
    • Create a program that writes a dictionary to a JSON file and reads it back.
  3. Custom Serialization:
    • Serialize a list of events with datetime objects to JSON and deserialize them back.

JSON is a powerful format for data exchange, and Python’s json module makes it easy to work with. Mastering this module is essential for handling APIs, configuration files, and more.

Next Lesson: APIs and Requests