Flask web server on Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Flask route response output

What is the output when you visit the root URL '/' of this Flask app running on Raspberry Pi?

Raspberry Pi

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello from Raspberry Pi!'

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

A Hello World!

B Hello from Raspberry Pi!

C 500 Internal Server Error

D 404 Not Found

💡 Hint

Look at the return value of the home() function.

The route '/' returns the string 'Hello from Raspberry Pi!'. Visiting this URL shows that exact text.

🧠 Conceptual

intermediate

Purpose of host='0.0.0.0' in Flask app

Why do we use host='0.0.0.0' when running a Flask app on Raspberry Pi?

A To allow the Flask app to accept connections from any device on the network

B To restrict the Flask app to only accept connections from localhost

C To enable HTTPS encryption automatically

D To run the Flask app on a random port

💡 Hint

Think about network accessibility from other devices.

Setting host='0.0.0.0' makes the Flask server listen on all network interfaces, allowing other devices to connect.

🔧 Debug

advanced

Identify the error in this Flask app code

What error will this Flask app code produce when run on Raspberry Pi?

Raspberry Pi

from flask import Flask
app = Flask(__name__)

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

if __name__ == '__main__':
    app.run(host='0.0.0.0')

A IndentationError: expected an indented block

B TypeError: app.route() missing required positional argument

C NameError: name 'app' is not defined

D No error, runs fine

💡 Hint

Check the indentation of the function body.

The function hello() has no indentation for its return statement, causing an IndentationError.

❓ Predict Output

advanced

Flask app with dynamic URL parameter output

What is the output when visiting '/user/Alice' on this Flask app running on Raspberry Pi?

Raspberry Pi

from flask import Flask
app = Flask(__name__)

@app.route('/user/<name>')
def user(name):
    return f'User: {name}'

if __name__ == '__main__':
    app.run(host='0.0.0.0')

A 404 Not Found

B User: <name>

C User: Alice

D User: user

💡 Hint

Look at how the URL parameter is used in the return string.

The route captures the name from the URL and returns it in the string 'User: {name}'.

📝 Syntax

expert

Identify the syntax error in this Flask app snippet

Which option correctly identifies the syntax error in this Flask app code snippet?

Raspberry Pi

from flask import Flask
app = Flask(__name__)

@app.route('/data')
def data():
    return {'value': 42}

if __name__ == '__main__':
    app.run(host='0.0.0.0')

A Flask app must import jsonify to return JSON data

B Missing colon after the function definition line

C app.run() missing required port argument

D Returning a dictionary directly causes a TypeError because Flask expects a string or Response object

💡 Hint

Think about what Flask accepts as a return value from route functions.

Returning a plain dictionary causes a TypeError because Flask cannot convert it automatically to a response.

Practice

1. What does the @app.route decorator do in a Flask web server on Raspberry Pi?

easy

A. It installs Flask on the Raspberry Pi.

B. It starts the Flask server to listen for requests.

C. It defines the URL path that triggers a specific function.

D. It stops the Flask server from running.

Solution

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

   This decorator tells Flask which URL path should run the function below it.

2. Step 2: Connect URL to function

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

3. Final Answer:

   It defines the URL path that triggers a specific function. -> Option C

4. Quick Check:

   @app.route sets URL path [OK]

Hint: Remember: route = URL path to function [OK]

Common Mistakes:

• Thinking it starts or stops the server
• Confusing it with installing Flask
• Assuming it runs the server automatically

2. Which of the following is the correct way to run a Flask app on Raspberry Pi so it is accessible from other devices on the network?

easy

A. app.run(host='0.0.0.0')

B. app.run(host='127.0.0.1')

C. app.run()

D. app.run(port=8080)

Solution

1. Step 1: Understand host parameter in app.run()

   By default, Flask listens only on localhost (127.0.0.1), meaning only the Pi itself can access it.

2. Step 2: Use host='0.0.0.0' to allow network access

   Setting host to '0.0.0.0' tells Flask to listen on all network interfaces, so other devices can connect.

3. Final Answer:

   app.run(host='0.0.0.0') -> Option A

4. Quick Check:

   host='0.0.0.0' allows network access [OK]

Hint: Use host='0.0.0.0' to share server on network [OK]

Common Mistakes:

• Using default host which blocks external access
• Confusing port with host
• Using localhost IP which restricts access

3. What will be the output when you visit http://raspberrypi.local/hello given this Flask code on Raspberry Pi?

from flask import Flask
app = Flask(__name__)

@app.route('/hello')
def hello():
    return 'Hello, Raspberry Pi!'

if __name__ == '__main__':
    app.run(host='0.0.0.0')

medium

A. Server does not start

B. 404 Not Found error

C. SyntaxError

D. Hello, Raspberry Pi!

Solution

1. Step 1: Check the route and function

   The route '/hello' is defined and returns the string 'Hello, Raspberry Pi!'.

2. Step 2: Accessing the URL

   Visiting /hello triggers the function and returns the string as the web page content.

3. Final Answer:

   Hello, Raspberry Pi! -> Option D

4. Quick Check:

   Route '/hello' returns greeting string [OK]

Hint: Match URL path to function return value [OK]

Common Mistakes:

• Expecting a 404 error if route is correct
• Thinking code has syntax errors
• Assuming server won't start with host='0.0.0.0'

4. Identify the error in this Flask code snippet intended to run on Raspberry Pi:

from flask import Flask
app = Flask(__name__)

@app.route('/status')
def status():
print('Server is running')

if __name__ == '__main__':
    app.run(host='0.0.0.0')

medium

A. Incorrect host value in app.run().

B. Missing indentation for the print statement inside the function.

C. Missing import statement for Flask.

D. Route decorator syntax is wrong.

Solution

1. Step 1: Check function body indentation

   The print statement inside the function must be indented to be part of the function block.

2. Step 2: Verify other parts

   Host value '0.0.0.0' is correct, Flask is imported, and route syntax is valid.

3. Final Answer:

   Missing indentation for the print statement inside the function. -> Option B

4. Quick Check:

   Python requires indentation inside functions [OK]

Hint: Indent function code properly in Python [OK]

Common Mistakes:

• Ignoring indentation errors
• Changing host unnecessarily
• Misreading route decorator syntax

5. You want your Flask app on Raspberry Pi to show different messages at / and /info. Which code correctly sets up these two routes?

hard

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

@app.route('/')
def home():
return 'Welcome!'

@app.route('/info')
def info():
return 'Raspberry Pi Info'

app.run(host='0.0.0.0')

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

@app.route('/')
def home():
return 'Welcome!'

@app.route('/')
def info():
return 'Raspberry Pi Info'

app.run(host='0.0.0.0')

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

@app.route('/info')
def home():
return 'Welcome!'

@app.route('/')
def info():
return 'Raspberry Pi Info'

app.run(host='0.0.0.0')

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

@app.route('/home')
def home():
return 'Welcome!'

@app.route('/info')
def info():
return 'Raspberry Pi Info'

app.run(host='0.0.0.0')

Solution

1. Step 1: Check route paths and functions

   from flask import Flask app = Flask(__name__) @app.route('/') def home(): return 'Welcome!' @app.route('/info') def info(): return 'Raspberry Pi Info' app.run(host='0.0.0.0') correctly uses '/' for home and '/info' for info, each with its own function returning the right message.

2. Step 2: Verify no route conflicts

   from flask import Flask app = Flask(__name__) @app.route('/') def home(): return 'Welcome!' @app.route('/') def info(): return 'Raspberry Pi Info' app.run(host='0.0.0.0') uses '/' twice, which causes conflict. from flask import Flask app = Flask(__name__) @app.route('/info') def home(): return 'Welcome!' @app.route('/') def info(): return 'Raspberry Pi Info' app.run(host='0.0.0.0') swaps routes and functions incorrectly. from flask import Flask app = Flask(__name__) @app.route('/home') def home(): return 'Welcome!' @app.route('/info') def info(): return 'Raspberry Pi Info' app.run(host='0.0.0.0') uses '/home' instead of '/'.

3. Final Answer:

   Option A correctly defines two distinct routes '/' and '/info'. -> Option A

4. Quick Check:

   Unique routes need unique paths [OK]

Hint: Use unique URLs for each route function [OK]

Common Mistakes:

• Defining two functions for the same route
• Swapping route paths and function names
• Using wrong URL paths like '/home' instead of '/'