Creating a Python REST API from Scratch

Prerequisites

Basic understanding of Python
Installed Python 3.6 or higher
Installed pip, a package manager for Python

Step 1: Set Up Your Project Environment

First, create a new folder for your project:

mkdir python-rest-api && cd python-rest-api

Then, create a virtual environment:

python3 -m venv env

Activate the virtual environment:

On macOS and Linux:

source env/bin/activate

On Windows:

.\env\Scripts\activate

Step 2: Install Flask and Other Dependencies

Install Flask, Flask-RESTful, SQLAlchemy, Flask-SQLAlchemy, and marshmallow using pip:

pip install flask flask-restful flask-sqlalchemy marshmallow

Step 3: Create a New Flask Application

Create a new file named app.py:

touch app.py

Open app.py in your text editor and add the following code:


        from flask import Flask

        

        app = Flask(__name__)

        

        @app.route('/')

        def hello_world():

            return 'Hello, World!'

        

        if __name__ == '__main__':

            app.run(debug=True)

Step 4: Create a Model with SQLAlchemy

We'll create a simple User model. Add the following code to app.py:


        from flask_sqlalchemy import SQLAlchemy

        

        app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////tmp/test.db'

        db = SQLAlchemy(app)

        

        class User(db.Model):

            id = db.Column(db.Integer, primary_key=True)

            username = db.Column(db.String(80), unique=True, nullable=False)

            email = db.Column(db.String(120), unique=True, nullable=False)

        

        def __repr__(self):

            return '' % self.username

Step 5: Create a Schema with Marshmallow

We'll use marshmallow to serialize and deserialize our User model. Add the following code to app.py:


        from marshmallow import Schema, fields

        

        class UserSchema(Schema):

            id = fields.Int(dump_only=True)

            username = fields.Str()

            email = fields.Email()

Step 6: Create a Resource with Flask-RESTful

We'll create a UserResource that will handle HTTP requests. Add the following code to app.py:


        from flask_restful import Resource, Api, request

        from marshmallow import ValidationError

        

        api = Api(app)

        user_schema = UserSchema()

        

        class UserResource(Resource):

            def get(self):

                users = User.query.all()

                return user_schema.dump(users, many=True)

            

            def post(self):

                try:

                    user = user_schema.load(request.json)

                    db.session.add(user)

                    db.session.commit()

                    return user_schema.dump(user)

                except ValidationError as err:

                    return err.messages, 400

        

        api.add_resource(UserResource, '/users')

Step 7: Test Your API

You can now test your API. Run your Flask application:

python app.py

You should be able to retrieve and create users by sending HTTP requests to http://localhost:5000/users.

For a GET request, you can simply visit the URL in your browser. For a POST request, you can use a tool like curl or Postman.

Here's an example of a POST request with curl:

curl -X POST -H "Content-Type: application/json" -d '{"username": "test", "email": "test@example.com"}' http://localhost:5000/users

This is a basic example of a Python REST API. There's a lot more you can do, like adding authentication, handling more types of requests, and adding more resources. But this should give you a good start.