Serving sensor data as JSON API in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a JSON API in the context of serving sensor data?

A JSON API is a way to send sensor data from a Raspberry Pi to other devices using a simple text format called JSON. It makes data easy to read and use by programs.

beginner

Why use JSON format to serve sensor data?

JSON is easy to read for both humans and computers. It is lightweight and works well over the internet, making it perfect for sharing sensor data from a Raspberry Pi.

beginner

Which Python library is commonly used on Raspberry Pi to create a simple JSON API?

Flask is a popular Python library used to create web servers that can serve JSON data easily on a Raspberry Pi.

intermediate

How do you convert sensor readings into JSON format in Python?

You can use Python's built-in json module. For example, use json.dumps() to turn a Python dictionary of sensor readings into a JSON string.

beginner

What is the role of an endpoint in a JSON API?

An endpoint is a specific URL on the Raspberry Pi server where sensor data is available. When you visit this URL, you get the sensor data in JSON format.

What does JSON stand for?

A JavaScript Online Network

B Java Standard Output Network

C JavaScript Object Notation

D Java Object Notation

JSON stands for JavaScript Object Notation, a lightweight data format.

Which Python library helps create a web server to serve JSON data on Raspberry Pi?

A Matplotlib

B NumPy

C Pandas

D Flask

Flask is a lightweight web framework used to create servers that can serve JSON data.

What is the main purpose of an API endpoint?

A To provide a URL where data can be accessed

B To store sensor hardware

C To convert data to binary

D To power the Raspberry Pi

An endpoint is a URL where clients can request and receive data.

Which Python function converts a dictionary to a JSON string?

A json.load()

B json.dumps()

C json.parse()

D json.read()

json.dumps() converts Python objects to JSON strings.

Why is JSON a good choice for sensor data sharing?

A It is easy to read and lightweight

B It is heavy and complex

C It only works on Raspberry Pi

D It requires special software to read

JSON is easy to read and lightweight, making it ideal for sharing data.

Explain how you would set up a simple JSON API on a Raspberry Pi to serve temperature sensor data.

Think about reading data, converting it, and making it available via a web address.

Describe the benefits of serving sensor data as a JSON API compared to other methods.

Consider why JSON is popular for data sharing.

Practice

1.

What is the main purpose of serving sensor data as a JSON API on a Raspberry Pi?

easy

A. To allow other devices to easily access sensor information in a standard format

B. To store sensor data only on the Raspberry Pi without sharing

C. To convert sensor data into images for display

D. To run heavy calculations on sensor data locally

Solution

1. Step 1: Understand JSON API purpose

   A JSON API provides data in a simple, standard format that other devices can read easily.

2. Step 2: Relate to sensor data sharing

   Serving sensor data as JSON means sharing sensor readings so other devices or apps can use them.

3. Final Answer:

   To allow other devices to easily access sensor information in a standard format -> Option A

4. Quick Check:

   JSON API shares sensor data easily [OK]

Hint: JSON API means sharing data in a simple format [OK]

Common Mistakes:

• Thinking JSON API stores data only locally
• Confusing JSON API with image or video output
• Assuming JSON API does heavy local processing

2.

Which of the following is the correct way to import Flask in a Python script on Raspberry Pi?

?

easy

A. import flask

B. import Flask

C. from Flask import flask

D. from flask import Flask

Solution

1. Step 1: Recall Flask import syntax

   The Flask class is imported from the flask module using: from flask import Flask

2. Step 2: Check options for correct case and syntax

   from flask import Flask matches correct syntax and case; others have wrong case or structure.

3. Final Answer:

   from flask import Flask -> Option D

4. Quick Check:

   Correct Flask import uses 'from flask import Flask' [OK]

Hint: Flask class is imported with 'from flask import Flask' [OK]

Common Mistakes:

• Using wrong capitalization like 'import Flask'
• Importing the whole module without accessing Flask class
• Mixing module and class names incorrectly

3.

What will be the output of this Flask route when accessed?

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

@app.route('/sensor')
def sensor_data():
    data = {'temperature': 22.5, 'humidity': 60}
    return jsonify(data)

# Assume app is running

medium

A. Error: jsonify not defined

B. {temperature: 22.5, humidity: 60}

C. {"temperature": 22.5, "humidity": 60}

D. ['temperature', 22.5, 'humidity', 60]

Solution

1. Step 1: Understand jsonify output

   jsonify converts Python dict to JSON string with keys in quotes and proper JSON format.

2. Step 2: Match output format

   {"temperature": 22.5, "humidity": 60} shows correct JSON string with keys and values properly formatted.

3. Final Answer:

   {"temperature": 22.5, "humidity": 60} -> Option C

4. Quick Check:

   jsonify returns JSON string with quoted keys [OK]

Hint: jsonify outputs JSON with quoted keys and values [OK]

Common Mistakes:

• Forgetting quotes around keys in JSON output
• Confusing Python dict print with JSON string
• Assuming jsonify returns Python list

4.

Identify the error in this Flask code snippet that serves sensor data as JSON:

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

@app.route('/data')
def data():
    sensor = {'temp': 25}
    return json.dumps(sensor)

app.run()

medium

A. json.dumps is used instead of jsonify

B. Flask app is not created correctly

C. Route decorator syntax is wrong

D. Missing import for Flask

Solution

1. Step 1: Check JSON response method

   Flask expects jsonify to create proper response with correct headers, not json.dumps.

2. Step 2: Identify error cause

   Using json.dumps returns a string without correct content-type, causing client issues.

3. Final Answer:

   json.dumps is used instead of jsonify -> Option A

4. Quick Check:

   Use jsonify, not json.dumps, for Flask JSON responses [OK]

Hint: Use jsonify for Flask JSON responses, not json.dumps [OK]

Common Mistakes:

• Returning json.dumps output directly in Flask
• Not importing jsonify
• Assuming json.dumps sets response headers

5.

You want to serve live temperature sensor data from a Raspberry Pi using Flask. Which approach correctly updates the JSON response with real sensor readings each time the API is called?

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

def read_temp_sensor():
    # Returns current temperature reading
    return 24.7

@app.route('/temp')
def temp():
    # Fill in here

app.run()

hard

A. temp = 24.7
return jsonify({'temperature': temp})

B. temp = read_temp_sensor()
return jsonify({'temperature': temp})

C. return jsonify({'temperature': read_temp_sensor})

D. return {'temperature': read_temp_sensor()} # Flask auto converts

Solution

1. Step 1: Call sensor function inside route

   We must call read_temp_sensor() to get current value each time the route is accessed.

2. Step 2: Return JSON response with current value

   Assign the value to a variable and pass it to jsonify to return proper JSON response.

3. Final Answer:

   temp = read_temp_sensor() return jsonify({'temperature': temp}) -> Option B

4. Quick Check:

   Call sensor function and jsonify result each request [OK]

Hint: Call sensor function inside route, then jsonify result [OK]

Common Mistakes:

• Returning function object instead of calling it
• Using fixed value instead of live sensor reading
• Returning dict without jsonify in Flask