Cycles through traffic light LEDs until paused by a button.

traffic_lights.py

from gpiozero import LED, Button
from time import sleep
from gpiozero import PushButton

red = LED(25)
yellow = LED(8)
green = LED(7)
button = Button(21)


# On the first press, start the loop, second press pause the loop, and third press resume the loop
paused = True

#This keeps track of what color we are on
color = "yellow"

#This keeps track of how long we've been on a color (value is in milliseconds)
t = 3000

#This is how long each LED will be on for
DURATION = 3000

#When the button is pressed, toggle the paused state
def pressed(button):
	if paused:
		paused = False
	else:
		paused = True

#Here is our main loop that will run forever
while True:
	sleep(0.01) #Sleep for only 10 milliseconds
	if not paused:
		if t < DURATION: #Are we still on the same LED as last time we ran the loop?
			t += 0.01 # Increase the counter by the 10 milliseconds we slept for, notice that we do not increase the counter while paused
		else: # We should move to the next LED
			t = 0 #Restart the count
			if color == "yellow": #Current color is yellow, next is red
				color = "red"
				yellow.off()
				red.on()
			elif color == "red": #Current color is red, next is green
				color = "green"
				red.off()
				green.on()
			elif color == "green": #Current color is green, next is yellow
				color = "yellow"
				green.off()
				yellow.on()