Button class with callbacks in Raspberry Pi - Mini Project: Build & Apply

Button class with callbacks

📖 Scenario: You are building a simple program to handle button presses on a Raspberry Pi. Buttons can do different things when pressed, so you want to create a Button class that can run a special function (called a callback) whenever the button is pressed.This is like having a doorbell that plays a different sound depending on who is at the door. The button press triggers the sound.

🎯 Goal: Create a Button class that stores a callback function. When the button is pressed, it should run the callback. You will then create a button instance, assign a callback, and simulate a button press to see the callback run.

📋 What You'll Learn

Create a Button class with an __init__ method that takes a callback parameter and stores it.

Add a press method to the Button class that calls the stored callback function.

Create a function called say_hello that prints 'Hello! Button pressed.'.

Create a Button instance called button with say_hello as the callback.

Call the press method on the button instance to run the callback.

Print the output of the callback when the button is pressed.

💡 Why This Matters

🌍 Real World

Buttons on Raspberry Pi or other devices often need to run specific code when pressed. Using callbacks lets you easily change what happens without rewriting the button code.

💼 Career

Understanding callbacks and event-driven programming is important for embedded systems, hardware interfacing, and GUI programming jobs.

1

Create the Button class with callback storage

Create a class called Button with an __init__ method that takes a parameter called callback and stores it in self.callback.

Raspberry Pi

# Create the Button class with __init__ method
# Your code here

Need a hint?

Remember, __init__ is the method that runs when you create a new object. Store the callback function in self.callback.

2

Add the press method to call the callback

Add a method called press to the Button class that calls the stored callback function using self.callback().

Raspberry Pi

class Button:
    def __init__(self, callback):
        self.callback = callback

    # Add the press method below
    # Your code here

Need a hint?

The press method should run the callback function stored in self.callback. Just call it like a normal function.

3

Create a callback function say_hello

Create a function called say_hello that prints 'Hello! Button pressed.' when called.

Raspberry Pi

class Button:
    def __init__(self, callback):
        self.callback = callback

    def press(self):
        self.callback()

# Create the say_hello function below
# Your code here

Need a hint?

Define a simple function that prints the message exactly as shown.

4

Create Button instance and press it to run callback

Create a Button instance called button with say_hello as the callback. Then call button.press() to run the callback and print the message.

Raspberry Pi

class Button:
    def __init__(self, callback):
        self.callback = callback

    def press(self):
        self.callback()

def say_hello():
    print('Hello! Button pressed.')

# Create button instance and press it below
# Your code here

Need a hint?

Create the button with say_hello as callback and call press() to see the message.