Button class with callbacks in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a callback function in the context of a Button class?

A callback function is a function that you assign to a button to be called automatically when the button is pressed or released. It lets the program respond to button events without constantly checking the button state.

beginner

Why use a Button class with callbacks instead of checking button state in a loop?

Using callbacks lets your program wait for button presses without wasting time checking repeatedly. It makes the code cleaner and more efficient, like setting an alarm instead of watching the clock all the time.

beginner

How do you assign a callback function to a Button object in Python on Raspberry Pi?

You create a Button object and then use its method (like when_pressed) to assign your function. For example: button.when_pressed = my_function

intermediate

What happens if you assign multiple callbacks to the same button event?

Usually, the last callback assigned will replace the previous one, so only one function runs when the button is pressed. To run multiple actions, you can write one callback that calls other functions.

intermediate

Explain debouncing in the context of button callbacks.

Debouncing is a way to ignore quick repeated signals caused by the button's mechanical parts bouncing. Without debouncing, your callback might run many times for one press. Libraries often handle this automatically.

What is the main purpose of a callback function in a Button class?

A To automatically run code when the button is pressed

B To check the button state continuously

C To create a new button on the screen

D To disable the button

A callback function runs automatically when the button event happens, like a press.

How do you assign a callback function to a button press event in Python on Raspberry Pi?

A button.press = my_function()

B button.on_press(my_function)

C button.callback(my_function)

D button.when_pressed = my_function

The correct syntax is assigning the function to button.when_pressed without parentheses.

What problem does debouncing solve in button callbacks?

A It prevents multiple triggers from one press

B It makes the button press faster

C It changes the button color

D It disables the button

Debouncing stops multiple signals caused by mechanical bouncing.

If you assign two different functions to button.when_pressed one after another, what happens?

A Both functions run in order

B Only the last assigned function runs

C Neither function runs

D The first function runs twice

The last assignment replaces the previous callback.

Why is using callbacks better than checking button state in a loop?

A Callbacks require more code

B Callbacks make the button press slower

C Callbacks save CPU time and make code cleaner

D Callbacks disable the button

Callbacks let the program wait for events efficiently without constant checking.

Describe how to create a Button object with a callback function that runs when the button is pressed on a Raspberry Pi.

Think about how you tell the button what to do when pressed.

Explain what debouncing is and why it is important when using button callbacks.

Imagine pressing a button and it acting like you pressed it many times quickly.