In today’s connected world, building APIs (Application Programming Interfaces) is essential for enabling communication between different applications. REST (Representational State Transfer) APIs, in particular, are popular because they follow simple, scalable, and stateless protocols using HTTP methods. In this guide, we will explore how to build REST APIs using Flask, a lightweight yet powerful web framework for Python.
REST API is an architectural style that allows interaction between web-based systems. It is built around HTTP requests to access and manipulate resources such as data or services. The key principles of REST include:
GET, POST, PUT, and DELETE to perform CRUD (Create, Read, Update, Delete) operations.Flask is a micro-framework for Python that’s both flexible and easy to use, making it ideal for building REST APIs. Here’s why Flask is great:
Before we start coding, let’s set up our development environment.
To install Flask, simply run:
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pip install Flask
You may also want to set up a virtual environment to keep your project dependencies organized:
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python -m venv venvsource venv/bin/activate # For macOS/Linux
venv\Scripts\activate # For Windows
Let’s start by creating a simple Flask app to ensure everything is working.
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from flask import Flask
app = Flask(__name__)
@app.route(‘/’)def home():
return “Welcome to the Flask API!”
if __name__ == ‘__main__’:
app.run(debug=True)
Run this script and open your browser at http://127.0.0.1:5000. You should see the message “Welcome to the Flask API!”
Let’s now add some REST API endpoints to our Flask app. A REST API consists of different routes that correspond to different resources and actions. For this guide, we’ll create an API for managing a list of books.
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books = [
{‘id’: 1, ‘title’: ‘1984’, ‘author’: ‘George Orwell’},
{‘id’: 2, ‘title’: ‘To Kill a Mockingbird’, ‘author’: ‘Harper Lee’}
]
@app.route(‘/api/books’, methods=[‘GET’])def get_books():
return {‘books’: books}
Here, we’ve created a /api/books endpoint that returns a list of books in JSON format.
Now let’s dive into handling the four main HTTP methods: GET, POST, PUT, and DELETE.
Here’s how you can handle each method in Flask:
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from flask import request, jsonify
@app.route(‘/api/books’, methods=[‘POST’])def add_book():
new_book = request.get_json()
books.append(new_book)
return {‘message’: ‘Book added successfully’}, 201
@app.route(‘/api/books/<int:book_id>’, methods=[‘PUT’])def update_book(book_id):
updated_data = request.get_json()
for book in books:
if book[‘id’] == book_id:
book.update(updated_data)
return {‘message’: ‘Book updated successfully’}
return {‘error’: ‘Book not found’}, 404
@app.route(‘/api/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 {‘message’: ‘Book deleted successfully’}
It’s important to validate the data sent to your API. You can use Flask extensions like Flask-RESTful or write custom validation logic.
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@app.route(‘/api/books’, methods=[‘POST’])def add_book():
new_book = request.get_json()
if not new_book or not ‘title’ in new_book or not ‘author’ in new_book:
return {‘error’: ‘Invalid input’}, 400
books.append(new_book)
return {‘message’: ‘Book added successfully’}, 201
This ensures that any new book must have a title and an author.
In Flask, you can control the HTTP status codes and return custom messages for both successful and failed API requests.
For example, returning a 404 error when a resource isn’t found:
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@app.route(‘/api/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:
return jsonify(book)
return {‘error’: ‘Book not found’}, 404
In real-world scenarios, APIs are typically connected to databases. You can use Flask with a wide variety of databases like SQLite, MySQL, and MongoDB. For SQLite integration, for instance, you can use Flask-SQLAlchemy.
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pip install Flask-SQLAlchemy
Here’s a quick setup with SQLite:
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from flask_sqlalchemy import SQLAlchemy
app.config[‘SQLALCHEMY_DATABASE_URI’] = ‘sqlite:///books.db’
db = SQLAlchemy(app)
class Book(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(80))
author = db.Column(db.String(80))
@app.route(‘/api/books’, methods=[‘GET’])def get_books():
books = Book.query.all()
return jsonify([{‘id’: book.id, ‘title’: book.title, ‘author’: book.author} for book in books])
Once your API is ready, you’ll want to deploy it. Flask APIs can be deployed on platforms like Heroku, AWS, or using Docker. Here’s a basic example for deploying on Heroku:
Create a Procfile with the following content:
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web: gunicorn app:app
Push your code to Heroku.
Visit your API on https://your-app-name.herokuapp.com.
Building REST APIs with Flask is simple yet powerful. Flask’s flexibility and Python’s simplicity make them a perfect combination for creating scalable web APIs. With this guide, you now have a foundational understanding of how to create, manage, and deploy REST APIs using Flask. Keep experimenting, and happy coding!
What API would you build next? Let us know in the comments!
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