Route decorator (@app.route) in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a route for the home page using Flask.

Flask

from flask import Flask
app = Flask(__name__)

@app.[1]('/')
def home():
    return "Welcome to the home page!"

Drag options to blanks, or click blank then click option'

Astart

Brun

Curl

Droute

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.run instead of @app.route

Forgetting the parentheses after the decorator method

Using @app.url which is not a Flask decorator

The @app.route decorator tells Flask which URL should trigger the home function.

2fill in blank

medium

Complete the code to create a route that responds to '/about' URL.

Flask

@app.[1]('/about')
def about():
    return "About us page"

Drag options to blanks, or click blank then click option'

Aroute

Bstart

Crun

Durl

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.run instead of @app.route

Missing the URL string inside the parentheses

Using @app.start which is not a Flask decorator

The @app.route decorator is used to bind the URL '/about' to the about function.

3fill in blank

hard

Fix the error in the route decorator to make the '/contact' page work.

Flask

@app.route[1]
def contact():
    return "Contact page"

Drag options to blanks, or click blank then click option'

A('/contact'

B('/contact')

C('/contact']

D['/contact']

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets instead of parentheses

Missing opening or closing parentheses

Mismatched quotes or brackets

The route decorator requires parentheses around the URL string. The correct syntax is @app.route('/contact').

4fill in blank

hard

Fill both blanks to create a route for '/user/<username>' that returns a greeting.

Flask

@app.[1]('/user/<[2]>')
def greet_user(username):
    return f"Hello, {username}!"

Drag options to blanks, or click blank then click option'

Aroute

Brun

Cusername

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.run instead of @app.route

Mismatching the variable name inside the URL and the function parameter

Using incorrect variable names inside the URL

The @app.route decorator defines the URL pattern. The part inside <> is the variable name, here username.

5fill in blank

hard

Fill all three blanks to create a route for '/post/' that returns the post ID.

Flask

@app.[1]('/post/<[2]:[3]>')
def show_post(post_id):
    return f"Post number {post_id}"

Drag options to blanks, or click blank then click option'

Aroute

Bint

Cpost_id

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using @app.run instead of @app.route

Forgetting the type converter before the variable name

Mismatching the variable name in the URL and function parameter

The @app.route decorator defines the route. The URL uses a converter int and variable name post_id matching the function parameter.

Practice

1. What does the @app.route decorator do in a Flask application?

easy

A. It connects a URL path to a specific function that runs when that URL is visited.

B. It creates a database connection for the app.

C. It styles the HTML pages served by Flask.

D. It starts the Flask server automatically.

Solution

1. Step 1: Understand the role of @app.route

   The decorator @app.route is used to link a URL path to a function in Flask.

2. Step 2: Identify what happens when the URL is visited

   When a user visits that URL, Flask runs the linked function to generate a response.

3. Final Answer:

   It connects a URL path to a specific function that runs when that URL is visited. -> Option A

4. Quick Check:

   @app.route links URL to function [OK]

Hint: Remember: @app.route maps URLs to functions [OK]

Common Mistakes:

• Thinking @app.route starts the server
• Confusing it with database setup
• Assuming it styles pages

2. Which of the following is the correct syntax to create a route for the URL path /home in Flask?

easy

A. @app.route('/home')\ndef home():\n return 'Welcome!'

B. app.route('/home')\ndef home():\n return 'Welcome!'

C. @app.route('/home')\nreturn 'Welcome!'

D. @app.route('/home')\ndef home:\n return 'Welcome!'

Solution

1. Step 1: Check the decorator syntax

   The correct decorator syntax uses @app.route('/home') placed immediately before a function definition.

2. Step 2: Verify the function definition and return statement

   The function must be defined with parentheses and a colon, and it returns a string response.

3. Final Answer:

   @app.route('/home')\ndef home():\n return 'Welcome!' -> Option A

4. Quick Check:

   Decorator + function with parentheses = correct syntax [OK]

Hint: Decorator needs @ and function needs () and : [OK]

Common Mistakes:

• Missing @ before app.route
• Omitting parentheses in function definition
• Placing return outside function

3. What will be the output when visiting the URL /user/42 given this Flask code?

@app.route('/user/<int:id>')
def show_user(id):
    return f"User ID is {id}"

medium

A. User ID is <int:id>

B. User ID is 42

C. 404 Not Found error

D. User ID is id

Solution

1. Step 1: Understand the route with variable part

   The route /user/<int:id> captures an integer from the URL and passes it as the argument id to the function.

2. Step 2: Check the function output

   The function returns a string with the captured id value inserted using an f-string.

3. Final Answer:

   User ID is 42 -> Option B

4. Quick Check:

   Variable URL part passes 42 to function [OK]

Hint: Variable parts in < > pass values to function [OK]

Common Mistakes:

• Thinking is printed literally
• Expecting a 404 error without reason
• Confusing variable name with string

4. Identify the error in this Flask route code:

@app.route('/hello')
def hello():
print('Hello World')
return 'Hello!'

medium

A. The return statement is outside the function.

B. The route decorator is missing parentheses.

C. The function name is invalid.

D. The function body is not indented properly.

Solution

1. Step 1: Check indentation inside the function

   Python requires the function body to be indented. Here, print and return are not indented under def hello():.

2. Step 2: Verify decorator and function syntax

   The decorator has correct parentheses and the function name is valid, so no errors there.

3. Final Answer:

   The function body is not indented properly. -> Option D

4. Quick Check:

   Python needs indented function bodies [OK]

Hint: Indent function code under def line [OK]

Common Mistakes:

• Forgetting to indent function body
• Removing parentheses from decorator
• Misnaming the function

5. You want to create a Flask route that accepts a username in the URL like /profile/john and returns Hello, john!. Which code correctly achieves this?

hard

A. @app.route('/profile/<username>')\ndef profile():\n return f'Hello, {username}!'

B. @app.route('/profile/')\ndef profile(username):\n return f'Hello, {username}!'

C. @app.route('/profile/<username>')\ndef profile(username):\n return f'Hello, {username}!'

D. @app.route('/profile/username')\ndef profile():\n return 'Hello, username!'

Solution

1. Step 1: Use variable URL part for username

   The route must capture username as a string variable using <username> in the URL.

2. Step 2: Define function with matching parameter and return greeting

   The function must accept username as a parameter and return the greeting using an f-string.

3. Final Answer:

   @app.route('/profile/<username>')\ndef profile(username):\n return f'Hello, {username}!' -> Option C

4. Quick Check:

   Variable URL + matching param + f-string = correct [OK]

Hint: Match variable name in route and function parameter [OK]

Common Mistakes:

• Using for a string username
• Not passing username parameter to function
• Hardcoding username in route path