Serving sensor data as JSON API in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Flask API endpoint?

Consider this Python Flask code running on a Raspberry Pi that reads a temperature sensor and serves the data as JSON. What will be the output when a client sends a GET request to /temperature?

Raspberry Pi

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

def read_temperature():
    return 23.5

@app.route('/temperature')
def temperature():
    temp = read_temperature()
    return jsonify({'temperature_celsius': temp})

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

A {"temp": 23.5}

B {"temperature_celsius": 23.5}

C 23.5

D Internal Server Error

💡 Hint

Look at the dictionary key used in jsonify.

The Flask endpoint returns a JSON response with key 'temperature_celsius' and value 23.5. So the output JSON string is {"temperature_celsius": 23.5}.

🧠 Conceptual

intermediate

Which HTTP method should be used to request sensor data from a JSON API?

You have a Raspberry Pi serving sensor data as a JSON API. Which HTTP method is the correct and standard way to request this data?

A GET

B DELETE

C PUT

D POST

💡 Hint

Think about which method is used to retrieve data without changing it.

GET is the standard HTTP method used to retrieve data from a server without modifying it.

🔧 Debug

advanced

What error does this Raspberry Pi Flask code raise?

This code tries to serve sensor data as JSON but has a bug. What error will it raise when running?

Raspberry Pi

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

def read_humidity():
    return 55

@app.route('/humidity')
def humidity():
    value = read_humidity()
    return jsonify({'humidity': value})

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

A SyntaxError

B TypeError

C KeyError

D No error, returns JSON

💡 Hint

Check the syntax of the argument passed to jsonify.

The code uses jsonify('humidity': value) which is invalid syntax. The correct syntax is jsonify({'humidity': value}). This causes a SyntaxError.

🚀 Application

advanced

How to add a timestamp to sensor JSON response?

You want to serve sensor data with a timestamp in the JSON response on your Raspberry Pi Flask API. Which code snippet correctly adds the current time in ISO format under key 'timestamp'?

Raspberry Pi

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

def read_light():
    return 300

@app.route('/light')
def light():
    value = read_light()
    # Add timestamp here
    return jsonify({})

A return jsonify({'light': value, 'timestamp': str(datetime.now)})

B return jsonify({'light': value, 'timestamp': datetime.isoformat()})

C return jsonify({'light': value, 'timestamp': datetime.now})

D return jsonify({'light': value, 'timestamp': datetime.now().isoformat()})

💡 Hint

Use datetime.now() to get current time, then convert to ISO string.

datetime.now() returns current datetime object. Calling isoformat() on it returns a string in ISO format. This is the correct way to add a timestamp string.

❓ Predict Output

expert

What is the output of this asynchronous sensor data API code?

This Raspberry Pi code uses async Flask to serve sensor data. What is the JSON output when calling /sensor?

Raspberry Pi

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

async def read_sensor():
    await asyncio.sleep(0.1)
    return {'temperature': 22.1, 'humidity': 48}

@app.route('/sensor')
async def sensor():
    data = await read_sensor()
    return jsonify(data)

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

A {"temperature": "22.1", "humidity": "48"}

B RuntimeError

C {"temperature": 22.1, "humidity": 48}

D Empty JSON {}

💡 Hint

Check the awaited function and returned dictionary keys and values.

The async function returns a dictionary with float and int values. jsonify converts it to JSON with numeric values, so output is {"temperature": 22.1, "humidity": 48}.