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

Flask Application Factory Pattern

📖 Scenario: You are building a simple Flask web app that can be easily configured and extended. To keep your app clean and organized, you will use the application factory pattern. This pattern helps you create Flask app instances with different settings.

🎯 Goal: Create a Flask app using the application factory pattern. You will start by setting up the app creation function, add configuration, register a simple route, and finally run the app.

📋 What You'll Learn

Create a function called create_app that returns a Flask app instance

Add a configuration setting DEBUG inside the app

Register a route / that returns the text Hello, Flask!

Run the app only if the script is executed directly

💡 Why This Matters

🌍 Real World

The application factory pattern is used in real Flask projects to create multiple app instances with different settings, such as testing, development, and production.

💼 Career

Understanding this pattern is important for backend developers working with Flask, as it helps write clean, scalable, and maintainable web applications.

1

Create the application factory function

Import Flask from flask and create a function called create_app that returns a new Flask app instance with the name __name__.

Flask

from flask import Flask

# Create the application factory function
# Your code here

Need a hint?

Think of create_app as a factory that builds and returns a new Flask app each time you call it.

2

Add configuration to the app

Inside the create_app function, set the app's DEBUG configuration to True before returning the app.

Flask

from flask import Flask

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

Need a hint?

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

3

Register a simple route

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 a route for '/' that returns 'Hello, Flask!'
    # Your code here

    return app

Need a hint?

Use the @app.route decorator to create a URL route and a function that returns the text.

4

Run the app when executed directly

Outside the create_app function, add the standard Python check if __name__ == '__main__':. Inside it, call create_app() to get the app instance and run it with app.run().

Flask

from flask import Flask

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

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

    return app

# Add code to run the app if this script is executed directly
# Your code here

Need a hint?

This check ensures the app runs only when you run this file directly, not when imported.