Python basics - Day 13

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Day 13 – JSON (JavaScript Object Notation)

Project: Build a “User Profile Data Manager” using JSON files

01. Learning Goal

By the end of this lesson, you will be able to:

Understand what JSON is and why it’s used
Convert between JSON and Python objects
Read from and write to JSON files
Manage structured data (like user profiles) with ease

02. Problem Scenario

You’re building an application that stores and retrieves user information (name, age, skills).

You want this data to be readable, lightweight, and compatible with APIs — this is where JSON comes in.

03. Step 1 – What is JSON?

JSON (JavaScript Object Notation) is a text-based data format used for data exchange.

It looks similar to Python dictionaries.

{
  "name": "Sabin",
  "age": 30,
  "skills": ["Python", "Flask", "React"]
}

Why it matters:
JSON is the standard format for communication between servers, databases, and APIs.

04. Step 2 – Working with JSON in Python

Python provides a built-in module json to handle JSON easily.

import json

05. Step 3 – Converting Between JSON and Python Objects

JSON → Python

import json

data = '{"name": "Sabin", "age": 30}'   # JSON string
py_obj = json.loads(data)                # Convert to dict
print(py_obj)                            # {'name': 'Sabin', 'age': 30}
print(py_obj["name"])                    # Sabin

Python → JSON

person = {"name": "Sabin", "age": 30}
json_str = json.dumps(person, ensure_ascii=False)
print(json_str)   # {"name": "Sabin", "age": 30}

06. Step 4 – Reading and Writing JSON Files

Write to file:

person = {"name": "Sabin", "age": 30, "skills": ["Python", "Flask"]}

with open("person.json", "w", encoding="utf-8") as f:
    json.dump(person, f, ensure_ascii=False, indent=2)

indent=2: pretty formatting with indentation
ensure_ascii=False: keeps non-English characters readable

Read from file:

with open("person.json", "r", encoding="utf-8") as f:
    data = json.load(f)

print(data)           # {'name': 'Sabin', 'age': 30, 'skills': ['Python', 'Flask']}
print(data["skills"]) # ['Python', 'Flask']

07. Step 5 – JSON with Lists

You can store multiple objects inside a list.

people = [
    {"name": "Tom", "age": 20},
    {"name": "Anna", "age": 22}
]

with open("people.json", "w", encoding="utf-8") as f:
    json.dump(people, f, ensure_ascii=False, indent=2)

with open("people.json", "r", encoding="utf-8") as f:
    loaded = json.load(f)

print(loaded[0]["name"])  # Tom

08. Step 6 – Practice Examples

Example 1: Convert Dictionary → JSON String

book = {"title": "Python Basics", "price": 25000}
json_str = json.dumps(book, ensure_ascii=False)
print(json_str)

Example 2: Convert JSON String → Dictionary

json_data = '{"title": "AI Guide", "author": "Sabin"}'
book = json.loads(json_data)
print(book["author"])

09. Step 7 – Mini Project: User Profile Data Manager

Create a small program to save and load user profile information using JSON.

import json

profile = {
    "name": "Sabin",
    "age": 30,
    "skills": ["Python", "Flask", "React"]
}

# Save profile
with open("profile.json", "w", encoding="utf-8") as f:
    json.dump(profile, f, ensure_ascii=False, indent=2)

# Load profile
with open("profile.json", "r", encoding="utf-8") as f:
    loaded = json.load(f)

print("Loaded Profile:")
for key, value in loaded.items():
    print(f"{key}: {value}")