Error handling in production in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a 404 error occurs in this Flask app?

Consider this Flask app snippet that handles 404 errors. What will the user see if they visit a non-existent page?

Flask

from flask import Flask, render_template
app = Flask(__name__)

@app.errorhandler(404)
def page_not_found(e):
    return render_template('404.html'), 404

@app.route('/')
def home():
    return 'Welcome Home!'

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

A The user sees the '404.html' page with a 404 status code.

B The user sees a default Flask error page with status 500.

C The user sees the home page content 'Welcome Home!'.

D The server crashes with a KeyError.

💡 Hint

Look at the @app.errorhandler decorator and what it returns.

The @app.errorhandler(404) decorator catches 404 errors and returns the custom '404.html' template with a 404 status code. This prevents the default Flask error page.

📝 Syntax

intermediate

Identify the syntax error in this Flask error handler

Which option correctly fixes the syntax error in this Flask error handler code?

Flask

from flask import Flask
app = Flask(__name__)

@app.errorhandler(500)
def internal_error(error):
    return 'Internal Server Error', 500

A Change @app.errorhandler(500) to @app.errorhandler('500').

B Remove the return statement inside the function.

C Add a colon at the end of the function definition line.

D Indent the return statement one level less.

💡 Hint

Check the function definition line syntax.

Python function definitions require a colon at the end of the def line. Missing colon causes a SyntaxError.

🔧 Debug

advanced

Why does this Flask app not show the custom 500 error page?

This Flask app tries to show a custom 500 error page but always shows the default Flask error page instead. What is the cause?

Flask

from flask import Flask, render_template
app = Flask(__name__)

@app.errorhandler(500)
def internal_error(e):
    return render_template('500.html'), 500

@app.route('/')
def home():
    1/0  # force error

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

A The error handler function is missing the error parameter.

B Because debug=True, Flask shows the debugger instead of the custom error page.

C The route '/' does not raise an error.

D The 500.html template is missing.

💡 Hint

Think about Flask's behavior when debug mode is on.

When debug=True, Flask shows the interactive debugger on errors instead of calling error handlers. To see custom error pages, debug must be off.

❓ state_output

advanced

What is the HTTP status code returned by this Flask error handler?

Given this Flask error handler, what status code will the client receive?

Flask

from flask import Flask, abort
app = Flask(__name__)

@app.errorhandler(403)
def forbidden(e):
    return 'Access Denied', 401

@app.route('/secret')
def secret():
    abort(403)

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

A 200

B 403

C 500

D 401

💡 Hint

Look at the return statement inside the error handler.

The error handler for 403 returns a response with status code 401, so the client receives 401 despite the error being 403.

🧠 Conceptual

expert

Why should you avoid showing detailed error messages in production Flask apps?

Which option best explains why detailed error messages should be hidden in production Flask applications?

A Detailed errors can reveal sensitive information that attackers could exploit.

B Detailed errors improve user experience by showing exact problems.

C Detailed errors reduce server load by avoiding extra logging.

D Detailed errors are required to comply with HTTP standards.

💡 Hint

Think about security risks of exposing internal details.

Showing detailed errors can expose code, server paths, or database info that attackers can use to find vulnerabilities. Production apps should show generic messages.