Module Lab: Building RESTful GET APIs with Flask

Learning Goals

• Implement RESTful API endpoints using Flask.
• Handle HTTP GET methods to serve resource data.
• Support query parameters and dynamic route segments.
• Return consistent JSON responses using jsonify().
• Follow RESTful conventions in route structure and response formatting.

Introduction

In this lab, you will build a Read-Only RESTful API to serve a list of products. The API will allow users to:

• Access a homepage route with a welcome message
• Retrieve all products via GET /products
• Fetch a specific product using GET /products/<id>
• Filter products by category using a query string (/products?category=books)

You’ll simulate a product catalog using an in-memory list of dictionaries, format all responses as JSON, and follow best practices for route design and error handling.

Setup Instructions

Fork and Clone the Repository

1. Go to the provided GitHub repository link.
2. Fork the repository to your GitHub account.
3. Clone the forked repository to your local machine:

git clone <repo-url>
cd course-8-module-4-get-api-flask

Install Dependencies

Ensure Python is installed:

python --version

Install Flask and dependencies using pipenv:

pipenv install
pipenv shell

Or with pip:

pip install flask

Tasks

Task 1: Define the Problem

You’re building a basic product catalog API. It should:

• Display a welcome message at /
• Serve all products with GET /products
• Retrieve individual products via GET /products/<id>
• Filter products by category using a query string (e.g. /products?category=books)

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Task 2: Determine the Design

The Flask API should:

• Use @app.route() decorators with methods=["GET"]
• Use request.args.get() to handle query parameters
• Return all output using jsonify()
• Return meaningful HTTP status codes (200, 404)

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Task 3: Develop the Code

Create app.py and start with the following structure:

from flask import Flask, jsonify, request

app = Flask(__name__)

# Mock data
products = [
    {"id": 1, "name": "Laptop", "price": 899.99, "category": "electronics"},
    {"id": 2, "name": "Book", "price": 14.99, "category": "books"},
    {"id": 3, "name": "Desk", "price": 199.99, "category": "furniture"},
]

# TODO: Implement homepage route that returns a welcome message
# TODO: Implement GET /products route that returns all products or filters by category
# TODO: Implement GET /products/<id> route that returns a product by ID or 404

if __name__ == "__main__":
    app.run(debug=True)

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Task 4: Test the API

Start the Flask development server:

python app.py

Test your endpoints using your browser, Postman, or curl:

• GET http://localhost:5000/
• GET http://localhost:5000/products
• GET http://localhost:5000/products/2
• GET http://localhost:5000/products?category=books

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Best Practices

• Use plural nouns for collection routes (e.g., /products)
• Normalize input (e.g., .lower()) when filtering by query string
• Use jsonify() for all responses
• Return:
  • 200 OK for successful GET requests
  • 404 Not Found if a product ID doesn’t exist
• Include inline comments to explain your logic

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Considerations

1. Input Validation

• Handle invalid query parameters or IDs with a clear error message.

2. Case Sensitivity in Filtering

• Normalize both category input and stored data to avoid mismatches.

3. Consistent Response Structure

• Ensure all responses follow the same JSON format.

4. Modular Code

• Keep logic clean and organized. As your API grows, consider separating routes into blueprints and data into separate modules.

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Conclusion

After completing this lab, you will:

✅ Understand RESTful GET route structure
✅ Build routes that serve both collections and single resources
✅ Use query strings to filter results
✅ Return structured JSON and meaningful HTTP responses

This lays the foundation for full CRUD APIs in the next module.