Stop a proccess started by os.system() in python

Question

I am currently making a data logging system using raspberry pi and I am using a push button to start/stop data logging. I am able to execute the python script "3ldrdatalog.py" by os.system(), but I cannot find a specific command to stop the script on the second button press.

Kindly help me with the code ! Thanks in advance

import RPi.GPIO as GPIO
from Adafruit_CharLCD import Adafruit_CharLCD
GPIO.setmode(GPIO.BCM)
GPIO.setup(13,GPIO.IN)
input = GPIO.input(13)
import time
import os
lcd = Adafruit_CharLCD()
#initialise a previous input variable to 0 (assume button not pressed last)
prev_input = 1
try:
   lcd.message('Press button')
   while True:
       #take a reading
       input = GPIO.input(13)

       #if the last reading was low and this one high, print
       if ((not prev_input) and input):
            print("Button pressed")
            lcd.clear()
            #this is the script that will be called (as root)
            os.system("python /home/pi/3ldrdatalog.py")
            #update previous input
            prev_input = input
            #slight pause to debounce
            time.sleep(0.05)
except KeyboardInterrupt:
   file.close()
   pass
finally:
    GPIO.cleanup()