old_contents: from gpiozero import LED
  import time
  
  # GPIO 24 ... LED ... 470 ohm resistor ... GND
  
  led = LED(24)
  try:
      led.blink()
      time.sleep(20)
  except KeyboardInterrupt:
      led.off()
  
  
new_contents: from gpiozero import LED
  import time
  
  # GPIO 24 ... LED ... 470 ohm resistor ... GND
  
  led = LED(24)
  try:
      led.blink()
      time.sleep(20)
  except KeyboardInterrupt:
      led.off()
  print "done"
  
subject: Print message on completion, to aid debugging