import RPi.GPIO as IO          # calling header file which helps us use GPIO’s of PI

import time                             # calling time to provide delays in program

IO.setwarnings(False)            #do not show any warnings

x=0                                         #integer for storing the duty cycle value

IO.setmode (IO.BCM)           #we are programming the GPIO by BCM pin numbers. (PIN35 as‘GPIO19’)

IO.setup(13,IO.OUT)         # initialize GPIO13 as an output.
IO.setup(19,IO.IN)             # initialize GPIO19 as an input.
IO.setup(26,IO.IN)             # initialize GPIO26 as an input.

p = IO.PWM(13,100)        #GPIO13 as PWM output, with 100Hz frequency
p.start(0)                            #generate PWM signal with 0% duty cycle

while 1:                             #execute loop forever

   p.ChangeDutyCycle(x)                 #change duty cycle for changing the brightness of LED.
      if(IO.input(26) == False):           #if button1 is pressed
          if(x<50):
             x=x+1                                 #increment x by one if x<50
             time.sleep(0.2)                   #sleep for 200ms

      if(IO.input(19) == False):         #if button2 is pressed
           if(x>0):
              x=x-1                                #decrement x by one if x>0
              time.sleep(0.2)                 #sleep for 200ms