Raspberry Pi PWM - Led Brightness Control

Controlling Brightness Of Led Using PWM with Raspberry Pi
Code :

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(21,GPIO.OUT)

p = GPIO.PWM(21,50)
p.start(0)

while True :
for i in range(100) :
p.ChangeDutyCycle(i)
time.sleep(0.05)
for i in range(100) :
p.ChangeDutyCycle(100-i)
time.sleep(0.05)


Output :