import RPi.GPIO as GPIO
import time

led = 23

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(led,GPIO.OUT)
p1 = GPIO.PWM(led, 50) # GPIO PWM with 50Hz
p1.start(0) # Initialization
print "CTRL+C = STOP program"

try:
    while True:
        for n in range(0,50,10):
            p1.ChangeDutyCycle(n)
            time.sleep(0.5)
        else:
            GPIO.output(led,GPIO.LOW)
except KeyboardInterrupt:
    GPIO.cleanup()  # must be executed before program stop