screen.py

import RPi.GPIO as GPIO
import time
import os

GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.IN, pull_up_down=GPIO.PUD_UP)

while True:
    input_state = GPIO.input(18)
    if input_state ==False:
        if open('tmp').readline().rstrip() == "0":
            os.system("sudo bash -c 'echo 1 > /sys/class/backlight/rpi_backlight/bl_power'")
            
            os.system("echo 1 > tmp")
        else:
            os.system("sudo bash -c 'echo 0 > /sys/class/backlight/rpi_backlight/bl_power'")
            os.system("echo 0 > tmp")