Making an object flash on and off constantly

[tomo_the_third]

Hi I'm looking to make an object flash on and off and I want to be able to the control the rate at which this happens. I can make it flick on and off randomly:

#make poles go on and off randomly
def mytimer(num):
# pick a 0 or a 1
on = random.choice([0, 1])
# Set the light's visibility to ON (1) or OFF (0)
poles.visible(on)

viz.callback(viz.TIMER_EVENT,mytimer)

viz.starttimer(0,0.5,viz.FOREVER)