What is Flask - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is Flask used for?

Flask is a popular tool in Python. What is its main purpose?

A To manage databases directly without code

B To build websites and web apps easily with Python

C To create desktop applications with graphical interfaces

D To analyze data and create charts

💡 Hint

Think about what web developers need to create websites.

Flask is a lightweight web framework in Python. It helps developers build web applications by providing tools to handle web requests and responses.

🧠 Conceptual

intermediate

Which feature is NOT part of Flask?

Flask provides many features. Which one is NOT included by default?

A Routing to handle different web pages

B Support for handling HTTP requests and responses

C Template rendering to create HTML pages

D Built-in database ORM (Object Relational Mapper)

💡 Hint

Flask is minimal and lets you add extra tools as needed.

Flask does not include a built-in ORM. Developers can add ORMs like SQLAlchemy separately.

❓ component_behavior

advanced

What happens when you run this Flask code?

Consider this Flask app code. What will the browser show when visiting '/'?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, Flask!'

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

A The browser shows the text: Hello, Flask!

B The browser shows a 404 Not Found error

C The browser shows a blank page

D The server crashes with an error

💡 Hint

Look at the route decorator and the returned string.

The route '/' is linked to the home function, which returns 'Hello, Flask!'. Visiting '/' shows this text.

📝 Syntax

advanced

Identify the syntax error in this Flask snippet

Which option correctly fixes the syntax error in this Flask code? from flask import Flask app = Flask(__name__) @app.route('/') def home() return 'Hi!' app.run()

A Add parentheses to app.run like app.run()

B Change @app.route('/') to @app.route('/home')

C Add a colon after def home():

D Indent the return statement one level less

💡 Hint

Check the function definition line carefully.

Python function definitions require a colon at the end of the def line. Missing colon causes SyntaxError.

❓ lifecycle

expert

What is the order of events when a Flask app handles a web request?

Put these steps in the correct order when Flask processes a web request: 1. Flask calls the view function 2. Browser sends HTTP request 3. Flask sends HTTP response back 4. Flask matches URL to route

A 1,2,3,4

B 1,3,2,4

C 2,1,3,4

D 1,2,4,3

💡 Hint

Think about what happens first: the browser sends a request or Flask matches routes?

First, the browser sends the HTTP request. Then Flask matches the URL to a route, calls the view function, and finally sends the response.

Practice

1. What is Flask primarily used for?

easy

A. Creating desktop applications

B. Building web applications with Python

C. Managing databases directly

D. Designing mobile apps

Solution

1. Step 1: Understand Flask's purpose

   Flask is a tool that helps developers create web applications using Python.

2. Step 2: Compare options with Flask's role

   Options A, C, and D describe other types of software development, not Flask's main use.

3. Final Answer:

   Building web applications with Python -> Option B

4. Quick Check:

   Flask = Web apps with Python [OK]

Hint: Flask = Python + web apps, not desktop or mobile [OK]

Common Mistakes:

• Thinking Flask is for desktop apps
• Confusing Flask with database tools
• Assuming Flask builds mobile apps

2. Which of the following is the correct way to start a basic Flask app?

easy

A. from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
return 'Hello, Flask!'

B. import flask
app = flask()

@app.route('/')
def home():
print('Hello, Flask!')

C. from flask import app
app = Flask()

@app.route('/')
def home():
return 'Hello, Flask!'

D. import Flask
app = Flask(__name__)

@app.route('/')
def home():
return 'Hello, Flask!'

Solution

1. Step 1: Check import and app creation

   from flask import Flask app = Flask(__name__) @app.route('/') def home(): return 'Hello, Flask!' correctly imports Flask and creates an app with Flask(__name__). Others have wrong imports or app creation.

2. Step 2: Verify route and return statement

   from flask import Flask app = Flask(__name__) @app.route('/') def home(): return 'Hello, Flask!' uses @app.route('/') and returns a string, which is correct Flask syntax.

3. Final Answer:

   Correct Flask app start code -> Option A

4. Quick Check:

   Correct import and route = from flask import Flask app = Flask(__name__) @app.route('/') def home(): return 'Hello, Flask!' [OK]

Hint: Import Flask and create app with Flask(__name__) [OK]

Common Mistakes:

• Using wrong import statements
• Calling flask() instead of Flask()
• Printing instead of returning response

3. What will this Flask route return when accessed?

from flask import Flask
app = Flask(__name__)

@app.route('/greet')
def greet():
    return 'Welcome to Flask!'

medium

A. Nothing, the route is not defined

B. A syntax error because of missing parentheses

C. A server error due to missing return statement

D. A web page showing 'Welcome to Flask!'

Solution

1. Step 1: Analyze the route definition

   The route '/greet' is defined with a function that returns the string 'Welcome to Flask!'.

2. Step 2: Understand Flask response behavior

   Flask sends the returned string as the response body, so visiting '/greet' shows that message.

3. Final Answer:

   A web page showing 'Welcome to Flask!' -> Option D

4. Quick Check:

   Route returns string response = A web page showing 'Welcome to Flask!' [OK]

Hint: Returned string is sent as web page content [OK]

Common Mistakes:

• Thinking return must be HTML tags
• Assuming missing parentheses cause error
• Believing route is undefined

4. Identify the error in this Flask app code:

from flask import Flask
app = Flask(__name__)

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

medium

A. Wrong app creation syntax

B. Incorrect import of Flask

C. Missing return statement in route function

D. Route decorator syntax error

Solution

1. Step 1: Check the route function body

   The function prints 'Hello World' but does not return anything, so Flask gets no response to send.

2. Step 2: Understand Flask route requirements

   Flask route functions must return a response string or object; printing does not send data to the client.

3. Final Answer:

   Missing return statement in route function -> Option C

4. Quick Check:

   Route must return response, not just print [OK]

Hint: Route functions must return, not print, response [OK]

Common Mistakes:

• Using print instead of return
• Assuming print sends response
• Ignoring missing return causes error

5. You want to create a Flask app that responds differently based on the URL path. Which feature helps you do this?

hard

A. Using multiple @app.route decorators with different paths

B. Using print statements inside one route

C. Creating multiple Flask app instances

D. Changing the Flask import statement

Solution

1. Step 1: Understand Flask routing

   Flask uses @app.route decorators to map different URL paths to different functions.

2. Step 2: Evaluate options for handling multiple paths

   Using multiple @app.route decorators with different paths allows different responses for each URL.

3. Final Answer:

   Using multiple @app.route decorators with different paths -> Option A

4. Quick Check:

   Multiple routes = different URL responses [OK]

Hint: Use multiple @app.route for different URLs [OK]

Common Mistakes:

• Thinking print changes URL response
• Creating multiple app instances unnecessarily
• Modifying import does not affect routing