2.3 · Extended Modules / Libraries

Goal: use libraries to talk to hardware without writing low-level drivers.

Why use a library

Most hardware comes with drivers and libraries that expose a high-level Python API. You import the library, call functions, and the library handles the low-level register reads and writes.

Example: a temperature sensor's datasheet has dozens of bytes to configure. The library's read_temperature() hides all of that.

Common library categories

Domain	Examples
Hardware GPIO	RPi.GPIO, gpiozero
Sensors	Adafruit_BME280, DHT11 libraries
Robotics	picamera2, motor-driver SDKs
Networking	requests, socket
Web	flask, django
Data	pandas, numpy
AI	tensorflow, pytorch, scikit-learn

The HKEAA expects awareness — you don't need to memorise APIs.

A simple Raspberry Pi LED example

from gpiozero import LED
from time import sleep

led = LED(17)             # GPIO pin 17

while True:
    led.on()
    sleep(1)
    led.off()
    sleep(1)

gpiozero hides PWM, voltage, current, register addresses. You think in on/off.

Installing libraries

pip install gpiozero
pip install requests

For micro:bit, the microbit module is preinstalled when you flash MicroPython.

Reading documentation

Most libraries publish reference docs on a website. Skills:

1. Find the getting-started page.
2. Look for code samples — copy and adapt.
3. Use the API reference as a dictionary.
4. Check examples repository for non-trivial use.

Combining libraries · IoT thermometer

from time import sleep
import board, adafruit_dht
import requests

dht = adafruit_dht.DHT22(board.D4)
URL = "https://example.com/api/temperature"

while True:
    try:
        t = dht.temperature
        h = dht.humidity
        requests.post(URL, json={"t": t, "h": h})
    except Exception:
        pass
    sleep(60)

This 10-line program reads a sensor and uploads to the cloud every minute — possible only because of three libraries (adafruit_dht, board, requests).

Ethical / quality concerns

• Trust the library? Check downloads / stars / community.
• Security? Pin versions, monitor for vulnerabilities.
• Licence? MIT/Apache fine; GPL imposes conditions.

Exam-style question

Q (5 marks): Describe how using an extended programming module / library simplifies writing programs that interact with sensors. Give one example.

Sample answer:

Extended modules (libraries) provide pre-written high-level functions that abstract away the low-level details of reading or writing to hardware registers, managing timings, and handling errors. The programmer can call a single function such as sensor.read_temperature() instead of writing dozens of lines that talk to the chip directly.

Example: on a Raspberry Pi, the Adafruit_DHT library exposes a read_retry(sensor, pin) function that returns the current humidity and temperature from a DHT22 sensor. Without the library, the programmer would need to handle the precise microsecond pulse-timing protocol the DHT22 uses, which is error-prone and unrelated to the educational purpose of the project.

Using libraries also reduces bugs, speeds up development, and makes code easier to read.

Key takeaways

• Libraries hide low-level details.
• Pip / package managers install them.
• Read the docs, copy examples.

Chapter 2 wrap-up & Elective 2C wrap-up

You can now build sensor-aware, event-driven programs and use libraries. Final self-test:

• Implement bubble, insertion, selection sort.
• Implement linear and binary search.
• Build stack, queue, linked list.
• Walk through a sense → think → act loop.
• Distinguish event-driven from sequential programming.

➡️ Back to: Electives overview