RaspberryPi Breathing LED Python Array

import wiringpi
import time
io = wiringpi.GPIO(wiringpi.GPIO.WPI_MODE_PINS)
io.pinMode(7,io.PUD_OFF)
io.pinMode(3,io.PUD_OFF)

while True:
        time.sleep(4)
        io.pinMode(7,io.PUD_DOWN)
        time.sleep(4)
        io.pinMode(3,io.PUD_DOWN)
        time.sleep(4)
        io.pinMode(7,io.PUD_OFF)
        time.sleep(4)
        io.pinMode(3,io.PUD_OFF)