Python json Module

The json module in Python provides functions for serializing and deserializing JSON (JavaScript Object Notation). JSON is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate.

Table of Contents

1. Introduction
2. Key Functions
   • json.dump
   • json.dumps
   • json.load
   • json.loads
3. Customization and Extending JSON
   • Custom Serialization
   • Custom Deserialization
4. Examples
   • Writing JSON to a File
   • Reading JSON from a File
   • Serializing a Python Object to JSON
   • Deserializing a JSON String to a Python Object
   • Custom JSON Encoder
   • Custom JSON Decoder
5. Real-World Use Case
6. Conclusion
7. References

Introduction

The json module provides an easy way to encode and decode data in JSON format. It is commonly used for data interchange between systems and applications.

Key Functions

json.dump

Serializes a Python object and writes it to a file.

import json

user = {'id': 1, 'firstName': 'John', 'lastName': 'Doe', 'email': 'john.doe@example.com'}
with open('user.json', 'w') as f:
    json.dump(user, f)

json.dumps

Serializes a Python object to a JSON formatted string.

import json

user = {'id': 1, 'firstName': 'John', 'lastName': 'Doe', 'email': 'john.doe@example.com'}
json_string = json.dumps(user)
print(json_string)

Output:

{"id": 1, "firstName": "John", "lastName": "Doe", "email": "john.doe@example.com"}

json.load

Deserializes a JSON formatted file to a Python object.

import json

with open('user.json', 'r') as f:
    user = json.load(f)
print(user)

Output:

{'id': 1, 'firstName': 'John', 'lastName': 'Doe', 'email': 'john.doe@example.com'}

json.loads

Deserializes a JSON formatted string to a Python object.

import json

json_string = '{"id": 1, "firstName": "John", "lastName": "Doe", "email": "john.doe@example.com"}'
user = json.loads(json_string)
print(user)

Output:

{'id': 1, 'firstName': 'John', 'lastName': 'Doe', 'email': 'john.doe@example.com'}

Customization and Extending JSON

Custom Serialization

You can define a custom encoder to handle complex Python objects.

import json

class User:
    def __init__(self, id, firstName, lastName, email):
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
        self.email = email

def user_encoder(obj):
    if isinstance(obj, User):
        return {'id': obj.id, 'firstName': obj.firstName, 'lastName': obj.lastName, 'email': obj.email}
    return json.JSONEncoder.default(obj)

user = User(1, 'John', 'Doe', 'john.doe@example.com')
json_string = json.dumps(user, default=user_encoder)
print(json_string)

Output:

{"id": 1, "firstName": "John", "lastName": "Doe", "email": "john.doe@example.com"}

Custom Deserialization

You can define a custom decoder to handle complex JSON data.

import json

class User:
    def __init__(self, id, firstName, lastName, email):
        self.id = id
        self.firstName = firstName
        self.lastName = lastName
        self.email = email

def user_decoder(dct):
    if 'id' in dct and 'firstName' in dct and 'lastName' in dct and 'email' in dct:
        return User(dct['id'], dct['firstName'], dct['lastName'], dct['email'])
    return dct

json_string = '{"id": 1, "firstName": "John", "lastName": "Doe", "email": "john.doe@example.com"}'
user = json.loads(json_string, object_hook=user_decoder)
print(user.id, user.firstName, user.lastName, user.email)

Output:

1 John Doe john.doe@example.com

Examples

Writing JSON to a File

import json

product = {'id': 101, 'name': 'Laptop', 'price': 999.99, 'description': 'A high-performance laptop.'}
with open('product.json', 'w') as f:
    json.dump(product, f)

Reading JSON from a File

import json

with open('product.json', 'r') as f:
    product = json.load(f)
print(product)

Output:

{'id': 101, 'name': 'Laptop', 'price': 999.99, 'description': 'A high-performance laptop.'}

Serializing a Python Object to JSON

import json

product = {'id': 101, 'name': 'Laptop', 'price': 999.99, 'description': 'A high-performance laptop.'}
json_string = json.dumps(product)
print(json_string)

Output:

{"id": 101, "name": "Laptop", "price": 999.99, "description": "A high-performance laptop."}

Deserializing a JSON String to a Python Object

import json

json_string = '{"id": 101, "name": "Laptop", "price": 999.99, "description": "A high-performance laptop."}'
product = json.loads(json_string)
print(product)

Output:

{'id': 101, 'name': 'Laptop', 'price': 999.99, 'description': 'A high-performance laptop.'}

Custom JSON Encoder

import json

class Product:
    def __init__(self, id, name, price, description):
        self.id = id
        self.name = name
        self.price = price
        self.description = description

class ProductEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Product):
            return {'id': obj.id, 'name': obj.name, 'price': obj.price, 'description': obj.description}
        return json.JSONEncoder.default(self, obj)

product = Product(101, 'Laptop', 999.99, 'A high-performance laptop.')
json_string = json.dumps(product, cls=ProductEncoder)
print(json_string)

Output:

{"id": 101, "name": "Laptop", "price": 999.99, "description": "A high-performance laptop."}

Custom JSON Decoder

import json

class Product:
    def __init__(self, id, name, price, description):
        self.id = id
        self.name = name
        self.price = price
        self.description = description

def product_decoder(dct):
    if 'id' in dct and 'name' in dct and 'price' in dct and 'description' in dct:
        return Product(dct['id'], dct['name'], dct['price'], dct['description'])
    return dct

json_string = '{"id": 101, "name": "Laptop", "price": 999.99, "description": "A high-performance laptop."}'
product = json.loads(json_string, object_hook=product_decoder)
print(product.id, product.name, product.price, product.description)

Output:

101 Laptop 999.99 A high-performance laptop.

Real-World Use Case

Configuration File Handling

JSON is commonly used for configuration files. Here is an example of reading and writing a configuration file in JSON format.

import json

config = {
    'database': {
        'host': 'localhost',
        'port': 3306,
        'user': 'admin',
        'password': 'admin123'
    },
    'debug': True
}

# Writing configuration to a file
with open('config.json', 'w') as f:
    json.dump(config, f, indent=4)

# Reading configuration from a file
with open('config.json', 'r') as f:
    config = json.load(f)

print(config)

Output:

{
    "database": {
        "host": "localhost",
        "port": 3306,
        "user": "admin",
        "password": "admin123"
    },
    "debug": true
}

Conclusion

The json module in Python provides an easy and efficient way to work with JSON data. It supports serializing and deserializing Python objects to and from JSON, making it a versatile tool for data interchange and configuration management.

References

• Python json module documentation