REST API for IoT device in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Flask REST API endpoint code?

Consider this simple Flask REST API code running on a Raspberry Pi controlling an LED. What will be the output when you send a GET request to /led/status?

Raspberry Pi

from flask import Flask, jsonify
app = Flask(__name__)

led_state = False

@app.route('/led/status')
def led_status():
    return jsonify({'led': 'on' if led_state else 'off'})

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

A {"led": "on"}

B {"led": "off"}

C 500 Internal Server Error

D 404 Not Found

💡 Hint

Look at the initial value of led_state.

The variable led_state is initially False, so the API returns {"led": "off"}.

🧠 Conceptual

intermediate

Which HTTP method is best to toggle an IoT device state?

You want to create a REST API to toggle an LED on a Raspberry Pi. Which HTTP method should you use to change the LED state?

A DELETE

B GET

C PUT

D POST

💡 Hint

Think about which method is used to create or change data on the server.

POST is used to send data to the server to change state, such as toggling an LED.

🔧 Debug

advanced

What error does this Raspberry Pi REST API code raise?

Examine this Flask code snippet for controlling a sensor. What error will it raise when running?

Raspberry Pi

from flask import Flask, request, jsonify
app = Flask(__name__)

sensor_value = 0

@app.route('/sensor', methods=['POST'])
def update_sensor():
    data = request.json
    return jsonify({'sensor': sensor_value})
    sensor_value = data['value']
    return jsonify({'sensor': sensor_value})

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

A UnboundLocalError: local variable 'sensor_value' referenced before assignment

B No error, returns updated sensor value

C TypeError: 'NoneType' object is not subscriptable

D KeyError: 'value'

💡 Hint

Look at how sensor_value is assigned inside the function.

Assigning to sensor_value inside the function without global makes Python treat it as local, but it is referenced before assignment.

📝 Syntax

advanced

Which option correctly defines a Flask route to turn on an LED?

Choose the correct Flask route definition to turn on an LED when a POST request is sent to /led/on.

A

@app.route('/led/on', methods=['POST'])
def led_on():
    turn_on_led()
    return 'LED is on'

B

@app.route('/led/on')
def led_on():
    turn_on_led()
    return 'LED is on'

C

@app.route('/led/on', method=['POST'])
def led_on():
    turn_on_led()
    return 'LED is on'

D

@app.route('/led/on', methods='POST')
def led_on():
    turn_on_led()
    return 'LED is on'

💡 Hint

Check the correct keyword and data type for HTTP methods in Flask routes.

The methods argument must be a list of strings. Option A uses the correct syntax.

🚀 Application

expert

What is the number of items in the JSON response from this Raspberry Pi REST API code?

This Flask API returns sensor readings as JSON. How many key-value pairs are in the JSON response?

Raspberry Pi

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/sensors')
def sensors():
    data = {
        'temperature': 22.5,
        'humidity': 45,
        'pressure': 1013
    }
    return jsonify(data)

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

A 2

B 1

C 3

D 4

💡 Hint

Count the keys in the data dictionary.

The dictionary has three keys: temperature, humidity, and pressure.