Route decorator (@app.route) in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing '/' route?

Given this Flask app code, what will the browser display when visiting the '/' URL?

Flask

from flask import Flask
app = Flask(__name__)

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

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

A The browser shows a 404 Not Found error

B The browser shows the text: Welcome Home!

C The browser shows a 500 Internal Server Error

D The browser shows a blank page

💡 Hint

Check what the @app.route('/') decorator does.

The @app.route('/') decorator tells Flask to run the home() function when the root URL '/' is accessed. The function returns 'Welcome Home!' which is shown in the browser.

📝 Syntax

intermediate

Which option causes a syntax error in route definition?

Identify which route decorator syntax is invalid in Flask.

A @app.route('/profile' methods=['GET'])

B @app.route('/contact', methods=['GET', 'POST'])

C @app.route('/about')

D @app.route('/login', methods=['POST'])

💡 Hint

Look for missing punctuation in the decorator.

Option A is missing a comma between the URL string and the methods argument, causing a syntax error.

❓ state_output

advanced

What is the output of this Flask route with variable?

What will be the output when visiting '/user/Alice' in this Flask app?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/user/<name>')
def user(name):
    return f'Hello, {name}!'

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

A Hello, user!

B Hello, <name>!

C Hello, Alice!

D 404 Not Found error

💡 Hint

The part captures the URL segment as a function argument.

The route captures 'Alice' as the name parameter and returns 'Hello, Alice!'.

🔧 Debug

advanced

Why does this Flask app raise a 404 error for '/hello'?

Given the code below, why does visiting '/hello' cause a 404 error?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/hello/')
def greet_slash():
    return 'Hi with slash!'

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

A Because '/hello' and '/hello/' are treated as different routes in Flask

B Because the greet() function has no return statement

C Because Flask requires routes to be decorated with @app.get() instead of @app.route()

D Because the app.run() is missing debug=True

💡 Hint

Check how Flask treats trailing slashes in routes.

Flask treats '/hello' and '/hello/' as different routes. If only '/hello/' is defined, visiting '/hello' gives 404 unless redirect is enabled.

🧠 Conceptual

expert

Which option correctly explains Flask route matching behavior?

Choose the correct statement about how Flask matches URLs to route decorators.

A Flask ignores the order of route definitions when matching URLs

B Flask automatically matches any URL starting with the route prefix regardless of trailing slashes

C Flask matches routes case-insensitively by default

D Flask matches routes exactly and does not consider trailing slashes unless configured otherwise

💡 Hint

Think about how Flask treats trailing slashes and case sensitivity.

Flask matches routes exactly including trailing slashes and is case-sensitive by default. It does not match prefixes automatically.