Serializing and deserializing JSON in Python

Introduction

We use JSON to save or send data in a simple text format. Serializing turns data into JSON text. Deserializing turns JSON text back into data.

Saving user settings to a file so they can be loaded later.

Sending data from a web app to a server.

Reading data from a file that was saved in JSON format.

Sharing data between different programs or devices.

Syntax

Python

import json

# Serialize (convert data to JSON string)
json_string = json.dumps(data)

# Deserialize (convert JSON string back to data)
data = json.loads(json_string)

json.dumps() converts Python data to a JSON string.

json.loads() converts a JSON string back to Python data.

Examples

This turns a Python dictionary into a JSON string.

Python

import json

# Serialize a dictionary to JSON string
data = {'name': 'Alice', 'age': 30}
json_str = json.dumps(data)
print(json_str)

This turns a JSON string back into a Python dictionary.

Python

import json

# Deserialize JSON string back to dictionary
json_str = '{"name": "Alice", "age": 30}'
data = json.loads(json_str)
print(data)

Lists can also be converted to JSON strings.

Python

import json

# Serialize a list to JSON string
numbers = [1, 2, 3, 4]
json_str = json.dumps(numbers)
print(json_str)

Sample Program

This program shows how to convert a Python dictionary to a JSON string and back again.

Python

import json

# Original data
person = {'name': 'Bob', 'age': 25, 'city': 'New York'}

# Serialize to JSON string
json_data = json.dumps(person)
print('Serialized JSON:', json_data)

# Deserialize back to Python dictionary
person_data = json.loads(json_data)
print('Deserialized data:', person_data)

Important Notes

JSON only supports basic data types like strings, numbers, lists, and dictionaries.

Python objects like sets or custom classes need special handling before serializing.

Use indent parameter in json.dumps() to make JSON output easier to read.

Summary

Serializing means converting Python data to JSON text.

Deserializing means converting JSON text back to Python data.

Use the json module's dumps() and loads() functions for this.