from RPi import GPIO
from time import sleep
import sys

led = 12

GPIO.setmode(GPIO.BOARD)
GPIO.setup(led, GPIO.OUT)

while True:
    sys.stdout.write("on. ")
    sys.stdout.flush()
    GPIO.output(led, True)
    sleep(0.2)

    sys.stdout.write("off. ")
    sys.stdout.flush()
    GPIO.output(led, False)
    sleep(0.2)