Application factory pattern preview in Flask - Mini Project: Build & Apply

Application factory pattern preview

📖 Scenario: You are building a simple Flask web app that can be created using a factory function. This pattern helps you make multiple app instances easily and keeps your code clean.

🎯 Goal: Create a Flask application using the application factory pattern. You will first set up the basic app creation function, then configure it, add a simple route, and finally run the app.

📋 What You'll Learn

Create a function called create_app that returns a Flask app instance

Inside create_app, create the Flask app with Flask(__name__)

Add a configuration variable DEBUG set to True inside create_app

Add a route / that returns the text 'Hello, Flask!'

Return the app instance from create_app

💡 Why This Matters

🌍 Real World

The application factory pattern is used in real Flask projects to create multiple app instances with different settings, useful for testing and deployment.

💼 Career

Understanding this pattern is important for backend developers working with Flask, as it is a common best practice in professional Flask applications.

1

Create the application factory function

Write a function called create_app that creates a Flask app instance with Flask(__name__) and returns it.

Flask

from flask import Flask

# Your code here

Need a hint?

Remember to import Flask first. Then define create_app and create the app inside it.

2

Add configuration to the app

Inside the create_app function, add a configuration variable DEBUG set to True on the app.config dictionary.

Flask

from flask import Flask

def create_app():
    app = Flask(__name__)
    # Set DEBUG to True
    # Your code here
    return app

Need a hint?

Use app.config['DEBUG'] = True to enable debug mode.

3

Add a route to the app

Inside the create_app function, add a route for / using @app.route('/'). Define a function called home that returns the string 'Hello, Flask!'.

Flask

from flask import Flask

def create_app():
    app = Flask(__name__)
    app.config['DEBUG'] = True
    # Add route for '/' here
    # Your code here
    return app

Need a hint?

Use the @app.route('/') decorator and define a function that returns the greeting.

4

Run the app using the factory

Outside the create_app function, create an app instance by calling create_app(). Then add the block if __name__ == '__main__': and inside it call app.run() to start the server.

Flask

from flask import Flask

def create_app():
    app = Flask(__name__)
    app.config['DEBUG'] = True

    @app.route('/')
    def home():
        return 'Hello, Flask!'

    return app

# Your code here

Need a hint?

Create the app by calling create_app() and run it inside the main guard.