Python script to turn off an HDMI-connected monitor on a Raspberry Pi

monitor.py

# This program monitors the screensaver and turns the monitor off
# when the screensaver blanks the screen, and back on again when
# the screensaver unblanks the screen.

import sys  # for exit()
import subprocess  # for command execution

# command to monitor the screensaver
MONITOR = "xscreensaver-command"
MONITOR_ARGS = [MONITOR, "-watch"]
# commands to turn the screen on and off
CONTROL = "vcgencmd"
CONTROL_BLANK = [CONTROL, "display_power", "0"]
CONTROL_UNBLANK = [CONTROL, "display_power", "1"]

def main():
	# start the screen monitoring program, pipe output back to us
	prog = subprocess.Popen(MONITOR_ARGS, stdout=subprocess.PIPE)

	try:  # use try/finally to clean up if an exception occurs
		while prog.poll() is None:  # subprocess still running
			# read a line from the monitoring program, 1 char at a time
			line = char = ""
			while char != "\n":
				line += char
				char = prog.stdout.read(1)
			# here we have a complete line; check the screensaver op
			if line.startswith("BLANK "):
				subprocess.call(CONTROL_BLANK)
			elif line.startswith("UNBLANK "):
				subprocess.call(CONTROL_UNBLANK)
		return prog.returncode

	finally:  # clean up
		prog.stdout.close()
		prog.kill()

sys.exit(main())