Blueprint URL prefixes in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the URL for the route in this Flask blueprint?

Given a Flask blueprint with a URL prefix, what URL will respond to the hello route?

Flask

from flask import Flask, Blueprint

bp = Blueprint('bp', __name__, url_prefix='/api')

@bp.route('/hello')
def hello():
    return 'Hello from blueprint!'

app = Flask(__name__)
app.register_blueprint(bp)

A /hello

B /api/hello

C /bp/hello

D /api

💡 Hint

Remember the url_prefix adds a prefix to all routes in the blueprint.

The blueprint has url_prefix='/api', so the route /hello becomes /api/hello when registered.

❓ state_output

intermediate

What is the output when accessing the root URL of this blueprint?

Consider this Flask blueprint with a URL prefix. What response will the client get when accessing /dashboard/?

Flask

from flask import Flask, Blueprint

dashboard = Blueprint('dashboard', __name__, url_prefix='/dashboard')

@dashboard.route('/')
def index():
    return 'Dashboard Home'

app = Flask(__name__)
app.register_blueprint(dashboard)

A Internal Server Error

B 404 Not Found

C Dashboard Home

D Method Not Allowed

💡 Hint

The route is defined at / inside the blueprint with prefix /dashboard.

Accessing /dashboard/ matches the blueprint's / route, returning 'Dashboard Home'.

📝 Syntax

advanced

Which option correctly sets a blueprint with a URL prefix and a route?

Choose the code snippet that correctly creates a Flask blueprint with URL prefix /shop and a route /items that returns 'Shop Items'.

A

bp = Blueprint('shop', __name__, url_prefix='/shop')
@bp.route('/items')
def items():
    return 'Shop Items'

B

bp = Blueprint('shop', __name__)
@bp.route('/shop/items')
def items():
    return 'Shop Items'

C

bp = Blueprint('shop', __name__, url_prefix='shop')
@bp.route('items')
def items():
    return 'Shop Items'

D

bp = Blueprint('shop', __name__, url_prefix='/shop')
@bp.route('items')
def items():
    return 'Shop Items'

💡 Hint

URL prefixes and routes must start with a slash / to be valid.

Option A correctly sets url_prefix='/shop' and route /items. Options C and D miss the leading slash in route or prefix. Option A does not use url_prefix.

🔧 Debug

advanced

Why does this blueprint route return 404 despite being registered?

Given this Flask app and blueprint, why does accessing /blog/post return 404?

Flask

from flask import Flask, Blueprint

blog = Blueprint('blog', __name__, url_prefix='/blog')

@blog.route('post')
def post():
    return 'Blog Post'

app = Flask(__name__)
app.register_blueprint(blog)

A The route decorator is missing a leading slash in 'post', so the route is invalid.

B The blueprint is not registered with the app.

C The URL prefix '/blog' is incorrect and should be '/blog/'.

D The function 'post' is missing a return statement.

💡 Hint

Check the route string in the decorator for correct syntax.

Flask requires route paths to start with a slash. Missing it causes the route not to register properly, leading to 404.

🧠 Conceptual

expert

How does Flask combine multiple blueprints with overlapping URL prefixes?

Suppose you register two blueprints with the same URL prefix /api. How does Flask handle routing when both define a route /status?

A Flask merges the two routes and calls both functions sequentially on access.

B Flask raises an error during app startup due to duplicate routes.

C Both routes are accessible under different URLs automatically to avoid conflict.

D The last registered blueprint's route overrides the previous one for <code>/api/status</code>.

💡 Hint

Think about how Flask registers routes internally and what happens if two routes have the same URL.

Flask does not raise an error but the last registered route for a URL overrides any previous one, so only one function handles requests to that URL.