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.

Practice

1. What is the main purpose of using a URL prefix in a Flask blueprint?

easy

A. To add a common path segment to all routes in the blueprint

B. To change the HTTP methods allowed for the routes

C. To register the blueprint with the Flask app

D. To define the template folder for the blueprint

Solution

1. Step 1: Understand what URL prefix means in Flask blueprints

   A URL prefix is a string added before all routes in a blueprint to group them under a common path.

2. Step 2: Identify the purpose of URL prefix

   This helps organize routes logically and keeps URLs clean by adding a shared path segment.

3. Final Answer:

   To add a common path segment to all routes in the blueprint -> Option A

4. Quick Check:

   URL prefix = common path for blueprint routes [OK]

Hint: URL prefix groups routes under one shared path [OK]

Common Mistakes:

• Confusing URL prefix with HTTP methods
• Thinking URL prefix registers the blueprint
• Mixing URL prefix with template folder settings

2. Which of the following is the correct way to set a URL prefix when creating a Flask blueprint?

easy

A. bp = Blueprint('bp', __name__, urlprefix='/admin')

B. bp = Blueprint('bp', __name__, prefix_url='/admin')

C. bp = Blueprint('bp', __name__, url_prefix='/admin')

D. bp = Blueprint('bp', __name__, route_prefix='/admin')

Solution

1. Step 1: Recall the correct parameter name for URL prefix

   The Flask Blueprint constructor uses the parameter named 'url_prefix' to set the prefix.

2. Step 2: Check each option for correct syntax

   Only bp = Blueprint('bp', __name__, url_prefix='/admin') uses 'url_prefix' exactly as Flask expects.

3. Final Answer:

   bp = Blueprint('bp', __name__, url_prefix='/admin') -> Option C

4. Quick Check:

   Correct parameter name is url_prefix [OK]

Hint: Use 'url_prefix' exactly when creating blueprint [OK]

Common Mistakes:

• Using incorrect parameter names like prefix_url
• Misspelling url_prefix as urlprefix
• Confusing route_prefix with url_prefix

3. Given this Flask blueprint code:

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

@bp.route('/items')
def items():
    return 'Shop Items'

What URL path will show the text 'Shop Items' when this blueprint is registered?

medium

A. /shop/items

B. /bp/items

C. /items

D. /shop/bp/items

Solution

1. Step 1: Understand how url_prefix affects route paths

   The url_prefix '/shop' is added before all routes in the blueprint.

2. Step 2: Combine prefix with route path

   The route '/items' becomes '/shop/items' when accessed in the app.

3. Final Answer:

   /shop/items -> Option A

4. Quick Check:

   URL = url_prefix + route path = /shop/items [OK]

Hint: URL = url_prefix + route path [OK]

Common Mistakes:

• Ignoring the url_prefix and using only route path
• Assuming blueprint name appears in URL
• Adding extra segments not defined

4. What is wrong with this Flask blueprint code?

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

@bp.route('data')
def data():
    return 'API Data'

medium

A. The function 'data' must accept a parameter

B. The url_prefix should be set when registering the blueprint, not here

C. The blueprint name 'bp' is invalid

D. The route path is missing a leading slash '/'

Solution

1. Step 1: Check the route decorator syntax

   Flask route paths must start with a leading slash '/' to be valid.

2. Step 2: Identify the missing slash in '@bp.route('data')'

   The route should be '@bp.route('/data')' to work correctly.

3. Final Answer:

   The route path is missing a leading slash '/' -> Option D

4. Quick Check:

   Route paths need leading '/' [OK]

Hint: Always start route paths with '/' [OK]

Common Mistakes:

• Omitting leading slash in route paths
• Thinking url_prefix is set only on registration
• Believing blueprint names have strict rules
• Assuming route functions need parameters without reason

5. You have two blueprints:

bp1 = Blueprint('bp1', __name__, url_prefix='/user')
@bp1.route('/profile')
def profile():
    return 'User Profile'

bp2 = Blueprint('bp2', __name__, url_prefix='/user')
@bp2.route('/settings')
def settings():
    return 'User Settings'

If both are registered in the app, what happens when you visit /user/settings?

hard

A. A routing conflict error occurs because both blueprints share the same prefix

B. The 'User Settings' page is shown correctly

C. The 'User Profile' page is shown instead

D. A 404 Not Found error occurs

Solution

1. Step 1: Understand blueprint URL prefixes and route paths

   Both blueprints share the same prefix '/user', but their routes differ: '/profile' and '/settings'.

2. Step 2: Check if routes overlap

   Since '/user/settings' matches only bp2's route, no conflict occurs.

3. Final Answer:

   The 'User Settings' page is shown correctly -> Option B

4. Quick Check:

   Same prefix allowed if routes differ [OK]

Hint: Same prefix okay if route paths differ [OK]

Common Mistakes:

• Assuming same prefix always causes conflict
• Confusing blueprint name with URL path
• Expecting 404 when route exists