traffic_pulse.py

from gpiozero import TrafficLights
from time import sleep
from itertools import cycle, chain
from signal import pause

lights = TrafficLights(12, 16, 19, pwm=True)

def slow(gen):
    for item in gen:
        yield item
        sleep(0.01)

def pulse():
    ramp = [i / 10 for i in range(10)]
    return cycle(chain(ramp, reversed(ramp)))


lights.red.source = slow(lights.green.values)
lights.amber.source = slow(lights.green.values)
lights.green.source = slow(pulse())
pause()