The_Official_Raspberry_Pi_-_Beginner’s_Book_Vol1,_2018 (1)

136 THE OFFICIAL RASPBERRY PI BEGINNER'S GUIDE

Reading a button in Python

Click the New button in Thonny to start a new project, and the Save button to save it as Button

Input. Using a GPIO pin as an input for a button is very similar to using a pin as an output for

an LED, but you need to import a different part of the GPIO Zero library. Type the following into

the script area:

from gpiozero import Button

button = Button( 2 )

To have code run when the button is pressed, GPIO Zero provides the wait_for_press

function. Type the following:

button.wait_for_press()

print("You pushed me!")

Click the Run button, then press the push-button switch. Your message will print to the

Python shell at the bottom of the Thonny window: you’ve successfully read an input from

the GPIO pin! If you want to try your program again, you’ll need to click the Run button again;

because there’s no loop in the program, it quits as soon as it has finished printing the message

to the shell.

To extend your program further, add the LED and resistor back into the circuit if you haven’t

already done so: remember to connect the resistor to the GPIO 25 pin and the long leg of the

LED, and the shorter leg of the LED to the ground rail on your breadboard.

To control an LED as well as read a button, you’ll need to import both the Button and LED

functions from the GPIO Zero library. You’ll also need the sleep function from the time

library. Go back to the top of your program, and type in the following as the new first two lines:

from gpiozero import LED

from time import sleep

Below the line button = Button(2), type:

led = LED( 25 )

Delete the line print("You pushed me!") and replace it with:

led.on()

sleep( 3 )

led.off()