Creating REST APIs with Flask

1. Introduction

Goal

In this tutorial, we will learn how to build REST APIs using Flask, a lightweight and powerful web framework for Python.

Learning Outcomes

By the end of this tutorial, you will understand what REST APIs are and how to create them using Flask. You will also learn how to use HTTP methods in Flask, how to process JSON data, and how to handle requests and responses.

Prerequisites

You will need a basic understanding of Python and JSON. Experience with Flask or web development is not necessary, but it would be helpful.

2. Step-by-Step Guide

What is a REST API?

REST (Representational State Transfer) is a standard for designing network applications. A REST API uses HTTP to perform operations (like GET, POST, PUT, DELETE) on data.

Installing Flask

First, you need to install Flask. You can do this with pip:

pip install flask

Creating a Flask App

To create a Flask app, you need to import Flask and create an instance of the Flask class:

from flask import Flask
app = Flask(__name__)

Creating Routes

In Flask, you can define routes using the @app.route() decorator and a function that returns the response:

@app.route('/')
def hello():
    return "Hello, World!"

Running the App

You can run the Flask app with app.run():

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

The debug=True argument enables debug mode, which shows detailed error messages if something goes wrong.

3. Code Examples

Creating a REST API

Now let's create a simple REST API for managing books. We'll use a list of dictionaries to store our books for simplicity.

from flask import Flask, jsonify, request

app = Flask(__name__)

books = [
    {'id': 1, 'title': 'The Great Gatsby', 'author': 'F. Scott Fitzgerald'},
    {'id': 2, 'title': '1984', 'author': 'George Orwell'},
    {'id': 3, 'title': 'To Kill a Mockingbird', 'author': 'Harper Lee'},
]

@app.route('/books', methods=['GET'])
def get_books():
    return jsonify({'books': books})

@app.route('/books', methods=['POST'])
def add_book():
    book = {'id': len(books) + 1, 'title': request.json['title'], 'author': request.json['author']}
    books.append(book)
    return jsonify({'book': book}), 201

@app.route('/books/<int:book_id>', methods=['GET'])
def get_book(book_id):
    book = next((book for book in books if book['id'] == book_id), None)
    if book is None:
        return jsonify({'error': 'Book not found'}), 404
    return jsonify({'book': book})

@app.route('/books/<int:book_id>', methods=['DELETE'])
def delete_book(book_id):
    global books
    books = [book for book in books if book['id'] != book_id]
    return '', 204

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

4. Summary

We've learned how to create a REST API with Flask, how to define routes, and how to handle different HTTP methods. We also learned how to process JSON data and how to use the jsonify function to convert Python objects to JSON.

5. Practice Exercises

1. Add a PUT method to the /books/<int:book_id> route to update a book's title and author. Test your API with curl or Postman.

2. Create a REST API for another type of data, like movies or songs. Include at least the GET, POST, and DELETE methods.

3. Add error handling to your API. For example, what should happen if someone tries to add a book without a title or author, or tries to update a book that doesn't exist?

Remember, practice is the key to mastering any skill, so make sure you experiment and try different things with your API. Happy coding!