Error handler decorators in Flask - Mini Project: Build & Apply

Error Handler Decorators in Flask

📖 Scenario: You are building a simple Flask web app that needs to handle errors gracefully. Instead of showing default error pages, you want to create custom error messages for common HTTP errors like 404 (Not Found) and 500 (Internal Server Error).

🎯 Goal: Build a Flask app that uses error handler decorators to catch 404 and 500 errors and return custom messages.

📋 What You'll Learn

Create a Flask app instance named app

Use the @app.errorhandler(404) decorator to handle 404 errors

Use the @app.errorhandler(500) decorator to handle 500 errors

Return a simple string message for each error handler function

💡 Why This Matters

🌍 Real World

Web apps need to handle errors gracefully to improve user experience and provide helpful feedback when something goes wrong.

💼 Career

Knowing how to use Flask error handler decorators is important for backend web developers to create robust and user-friendly applications.

1

Create the Flask app instance

Import Flask from flask and create a Flask app instance called app.

Flask

# Import Flask and create app instance
# Your code here

Need a hint?

Use Flask(__name__) to create the app instance.

2

Add a 404 error handler decorator

Use the @app.errorhandler(404) decorator to create a function called handle_404 that returns the string 'Page not found'.

Flask

from flask import Flask
app = Flask(__name__)

# Add 404 error handler decorator and function
# Your code here

Need a hint?

The function must accept one parameter, usually named error.

3

Add a 500 error handler decorator

Use the @app.errorhandler(500) decorator to create a function called handle_500 that returns the string 'Internal server error'.

Flask

from flask import Flask
app = Flask(__name__)

@app.errorhandler(404)
def handle_404(error):
    return 'Page not found'

# Add 500 error handler decorator and function
# Your code here

Need a hint?

Like the 404 handler, the function must accept one parameter error.

4

Add a simple route and run the app

Add a route for '/' that returns 'Welcome to the homepage'. Then add the if __name__ == '__main__' block to run the app with app.run().

Flask

from flask import Flask
app = Flask(__name__)

@app.errorhandler(404)
def handle_404(error):
    return 'Page not found'

@app.errorhandler(500)
def handle_500(error):
    return 'Internal server error'

# Add a route for '/' and run the app
# Your code here

Need a hint?

The route function should be named home and return the welcome string.