Blueprint routes and templates in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing a Blueprint route?

Given this Flask Blueprint setup, what will the browser display when visiting /blog/?

Flask

from flask import Blueprint, render_template_string

blog = Blueprint('blog', __name__, template_folder='templates')

@blog.route('/')
def index():
    return render_template_string('<h1>Blog Home</h1>')

# Assume app.register_blueprint(blog, url_prefix='/blog') is done

A 404 Not Found error

B <h1>Blog Home</h1>

C 500 Internal Server Error

D Empty page with status 200

💡 Hint

Think about how Blueprint routes are registered with a URL prefix.

The Blueprint 'blog' is registered with the prefix '/blog'. The route '/' inside the Blueprint corresponds to '/blog/' in the app. The function returns a simple HTML heading, so the browser shows '

Blog Home

'.

📝 Syntax

intermediate

Identify the syntax error in Blueprint route definition

Which option contains a syntax error in defining a Flask Blueprint route?

Flask

from flask import Blueprint

api = Blueprint('api', __name__)

@api.route('/data')
def get_data():
    return 'Data response'

A

@api.route('/data')
def get_data()
    return 'Data response'

B

@api.route('/data')
def get_data():
    return 'Data response'

C

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D

api.route('/data')
def get_data():
    return 'Data response'

💡 Hint

Check for missing colons and indentation.

Option A is missing a colon after the function definition, causing a SyntaxError. Options A, C, and D are identical and correct.

❓ state_output

advanced

What template is rendered by this Blueprint route?

Given this Blueprint and template setup, what will be rendered when visiting /shop/?

Flask

from flask import Blueprint, render_template

shop = Blueprint('shop', __name__, template_folder='shop_templates')

@shop.route('/')
def home():
    return render_template('home.html')

# Assume app.register_blueprint(shop, url_prefix='/shop')

# Content of shop_templates/home.html:
# <h2>Welcome to the Shop</h2>

A <h2>Welcome to the Shop</h2>

B <h1>Shop Home</h1>

C TemplateNotFound error

D Empty response with status 200

💡 Hint

Check the template folder specified in the Blueprint and the template file name.

The Blueprint specifies 'shop_templates' as its template folder. The route renders 'home.html' from that folder, which contains '

Welcome to the Shop

'. So this HTML is rendered.

🔧 Debug

advanced

Why does this Blueprint route cause a 404 error?

Consider this Blueprint code and registration. Why does visiting /admin/dashboard return 404?

Flask

from flask import Blueprint

admin = Blueprint('admin', __name__)

@admin.route('/dashboard')
def dashboard():
    return 'Admin Dashboard'

# In main app:
# app.register_blueprint(admin, url_prefix='/admin/')

A The function 'dashboard' is missing a return statement.

B The route '/dashboard' inside Blueprint is incorrect syntax.

C The url_prefix has a trailing slash causing route mismatch.

D Blueprint name 'admin' conflicts with Flask reserved keywords.

💡 Hint

Check how url_prefix with trailing slash affects route matching.

Using url_prefix='/admin/' adds a trailing slash to the prefix. Flask concatenates this with the route '/dashboard' resulting in '/admin//dashboard' which does not match '/admin/dashboard'. This causes a 404 error. Removing the trailing slash in url_prefix fixes the issue.

🧠 Conceptual

expert

How does Flask resolve templates in nested Blueprints?

If you have a Blueprint 'store' with template_folder='templates/store' and inside it a nested Blueprint 'products' with template_folder='templates/store/products', which template path will Flask look for when rendering render_template('list.html') inside 'products' Blueprint?

A templates/list.html

B templates/store/products/templates/list.html

C templates/store/list.html

D templates/store/products/list.html

💡 Hint

Blueprints use their own template_folder as base for render_template calls inside them.

Each Blueprint uses its own template_folder as the root for templates. The nested 'products' Blueprint has template_folder='templates/store/products', so render_template('list.html') looks inside that folder. It does not fallback to parent Blueprint folders automatically.

Practice

1. What is the main purpose of using a Blueprint in a Flask application?

easy

A. To handle user authentication automatically

B. To organize routes and templates into reusable components

C. To create a new Flask app instance

D. To connect Flask with a database

Solution

1. Step 1: Understand Blueprint role

   A Blueprint groups related routes and templates to keep code organized.

2. Step 2: Compare other options

   Connecting to databases, creating app instances, or handling authentication are separate tasks.

3. Final Answer:

   To organize routes and templates into reusable components -> Option B

4. Quick Check:

   Blueprint = organize routes/templates [OK]

Hint: Blueprints group routes/templates for better app structure [OK]

Common Mistakes:

• Thinking Blueprint creates the app instance
• Confusing Blueprint with database connection
• Assuming Blueprint handles authentication automatically

2. Which of the following is the correct way to register a Blueprint named blog with a Flask app app using the URL prefix /blog?

easy

A. app.register_blueprint(blog, url_prefix='/blog')

B. app.register_blueprint('/blog', blog)

C. app.register_blueprint(blog.prefix('/blog'))

D. app.register_blueprint(blog, prefix_url='/blog')

Solution

1. Step 1: Recall correct method signature

   The method is register_blueprint(blueprint, url_prefix='...').

2. Step 2: Check options for correct syntax

   Only app.register_blueprint(blog, url_prefix='/blog') uses the correct method and parameter names.

3. Final Answer:

   app.register_blueprint(blog, url_prefix='/blog') -> Option A

4. Quick Check:

   register_blueprint with url_prefix = app.register_blueprint(blog, url_prefix='/blog') [OK]

Hint: Use url_prefix parameter to set Blueprint URL base [OK]

Common Mistakes:

• Swapping parameter order
• Using wrong parameter name like prefix_url
• Calling prefix as a method on Blueprint

3. Given this Blueprint code:

from flask import Blueprint, render_template
blog = Blueprint('blog', __name__, template_folder='templates')

@blog.route('/post')
def show_post():
    return render_template('post.html')

And this main app code:

from flask import Flask
app = Flask(__name__)
app.register_blueprint(blog, url_prefix='/blog')

What URL should you visit to see the post.html template rendered?

medium

A. /blog

B. /post

C. /blog/post

D. /post/blog

Solution

1. Step 1: Understand route and url_prefix

   The Blueprint route is '/post', and the Blueprint is registered with prefix '/blog'.

2. Step 2: Combine prefix and route

   The full URL becomes '/blog/post' to access the route.

3. Final Answer:

   /blog/post -> Option C

4. Quick Check:

   url_prefix + route = /blog/post [OK]

Hint: Combine url_prefix and route for full URL [OK]

Common Mistakes:

• Ignoring url_prefix and using only route
• Swapping url_prefix and route order
• Assuming url_prefix is not added to route

4. What is wrong with this Blueprint registration code?

from flask import Flask
app = Flask(__name__)
app.register_blueprint(blog, prefix='/blog')

medium

A. You cannot register blueprints in Flask

B. Blueprint must be registered before app creation

C. Blueprint name must be 'app' to register

D. The parameter should be url_prefix, not prefix

Solution

1. Step 1: Check parameter name in register_blueprint

   The correct parameter to set URL prefix is url_prefix, not prefix.

2. Step 2: Validate other options

   Blueprints register after app creation; name can be anything; Flask supports blueprints.

3. Final Answer:

   The parameter should be url_prefix, not prefix -> Option D

4. Quick Check:

   Correct param is url_prefix [OK]

Hint: Use url_prefix, not prefix, when registering Blueprint [OK]

Common Mistakes:

• Using prefix instead of url_prefix
• Trying to register Blueprint before app exists
• Thinking Blueprint name must be 'app'

5. You have two Blueprints, admin and user, both with a route /dashboard. How can you register them in your Flask app to avoid URL conflicts and keep URLs clear?

hard

A. Register each Blueprint with a different url_prefix, like /admin and /user

B. Rename one Blueprint's route to /dashboard2

C. Register both Blueprints without any url_prefix

D. Use the same url_prefix for both Blueprints

Solution

1. Step 1: Understand URL conflicts

   Both Blueprints have the same route /dashboard, which causes conflicts if no prefix is used.

2. Step 2: Use url_prefix to separate routes

   Assigning different url_prefix values like /admin and /user keeps URLs unique and organized.

3. Final Answer:

   Register each Blueprint with a different url_prefix, like /admin and /user -> Option A

4. Quick Check:

   Different url_prefix avoids route conflicts [OK]

Hint: Use unique url_prefix for each Blueprint to avoid conflicts [OK]

Common Mistakes:

• Not using url_prefix and causing route clashes
• Renaming routes manually instead of using prefixes
• Using same url_prefix for multiple Blueprints