WAI Forward Developer Blog

How to Create a REST API

By: WAI Forward ltd on March 10, 2025

REST APIs (Representational State Transfer Application Programming Interfaces) allow applications to communicate over the internet. They are widely used in web development, mobile apps, and cloud services to enable seamless data exchange.

In this guide, we’ll walk through the step-by-step process of creating a REST API using Python and Flask.

Why Build a REST API?

REST APIs provide several benefits, including:

Scalability: RESTful services can handle large amounts of traffic efficiently.
Interoperability: APIs work across different platforms and languages.
Flexibility: Supports multiple data formats like JSON and XML.

Prerequisites

Before we start, ensure you have:

Python (3.x recommended)
Flask (`pip install flask`)
Postman (optional, for testing API requests)

Step 1: Setting Up Flask

Create a new project folder and navigate into it:

mkdir flask_api
cd flask_api

Inside the folder, create a new Python file named app.py and add the following code:

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/')
def home():
    return jsonify({"message": "Welcome to the REST API!"})

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

Step 2: Defining API Endpoints

Let’s create a simple API that manages a list of users.

users = [
    {"id": 1, "name": "Alice"},
    {"id": 2, "name": "Bob"}
]

@app.route('/users', methods=['GET'])
def get_users():
    return jsonify(users)

Step 3: Retrieving a Single User

We can allow clients to retrieve a user by ID.

from flask import request

@app.route('/users/<int:user_id>', methods=['GET'])
def get_user(user_id):
    user = next((u for u in users if u["id"] == user_id), None)
    return jsonify(user if user else {"error": "User not found"}), 404 if not user else 200

Step 4: Adding a New User

We can enable clients to add new users using a POST request.

@app.route('/users', methods=['POST'])
def add_user():
    data = request.get_json()
    new_user = {"id": len(users) + 1, "name": data["name"]}
    users.append(new_user)
    return jsonify(new_user), 201

Step 5: Updating a User

Updating a user’s information is done using a PUT request.

@app.route('/users/<int:user_id>', methods=['PUT'])
def update_user(user_id):
    data = request.get_json()
    user = next((u for u in users if u["id"] == user_id), None)
    if not user:
        return jsonify({"error": "User not found"}), 404
    user["name"] = data["name"]
    return jsonify(user)

Step 6: Deleting a User

To remove a user, we use a DELETE request.

@app.route('/users/<int:user_id>', methods=['DELETE'])
def delete_user(user_id):
    global users
    users = [u for u in users if u["id"] != user_id]
    return jsonify({"message": "User deleted"}), 200

Step 7: Running and Testing the API

Start the API server by running:

python app.py

Use Postman or `curl` to test API endpoints.

Best Practices for REST API Development

Use Proper Status Codes: Return appropriate HTTP status codes like 200 (OK), 201 (Created), 400 (Bad Request), and 404 (Not Found).
Implement Authentication: Use API keys, OAuth, or JWT for secure access.
Follow REST Principles: Use clear, resource-oriented endpoints.
Log API Requests: Monitor API activity using logging frameworks.

FAQs

What is the difference between REST and SOAP? REST is lightweight and uses JSON, while SOAP is XML-based and more complex.
Can I use Flask for production REST APIs? Yes, but use Gunicorn or uWSGI with Nginx for better performance.
How do I secure my API? Implement authentication, rate limiting, and input validation.
Can I connect my API to a database? Yes, use Flask-SQLAlchemy to interact with a database.
How do I handle API versioning? Use versioned URLs like `/api/v1/users`.

Conclusion

Creating a REST API with Flask is simple and effective. By following best practices and adding authentication and validation, you can build scalable APIs for various applications.

Start building your own REST API today and enhance your web and mobile projects!

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