Change background to red on low battery.

battery_check.py

#!/usr/bin/env python3

import os
import time
import argparse
from subprocess import check_call

def cli_options():
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--percentage", "-p", help="battery %% warning", default=8, type=int,
        )
    parser.add_argument(
        "--level-file", "-l", help="battery level info file",
        default="/sys/class/power_supply/BAT0/capacity", type=str,
        )
    parser.add_argument(
        "--background", "-b", help="background image",
        default="%s/.bg.jpg" % os.getenv("HOME"), type=str,
        )
    parser.add_argument(
        "--warning", "-w", help="warning background image",
        default="%s/.bg-warning.jpg" % os.getenv("HOME"), type=str,
        )
    parser.add_argument(
        "--lock-ok", "-o", help="lock file",
        default="%s/.bg-ok.lock" % os.getenv("HOME"), type=str,
        )
    parser.add_argument(
        "--lock-warning", "-i", help="lock file",
        default="%s/.bg-warning.lock" % os.getenv("HOME"), type=str,
        )
    parser.add_argument(
        "--setter", "-s", help="background setter program",
        default="/usr/bin/feh --bg-fill", type=str,
        )
    return parser.parse_args()

def remove_lock(lock):
    try:
        os.unlink(lock)
    except FileNotFoundError:
        pass

def set_wallpaper(setter, bg_file):
    setter = setter.split(" ")
    setter.append(bg_file)
    check_call(setter)

def main():
    options = cli_options()

    # Reset state.
    remove_lock(options.lock_ok)
    remove_lock(options.lock_warning)

    while True:
        with open(options.level_file, "r") as f:
            current_level = int(f.read())

        if current_level <= options.percentage and \
                not os.path.exists(options.lock_warning):
            set_wallpaper(options.setter, options.warning)
            remove_lock(options.lock_ok)
            open(options.lock_warning, "a").close()
        elif current_level > options.percentage and \
                not os.path.exists(options.lock_ok):
            set_wallpaper(options.setter, options.background)
            remove_lock(options.lock_warning)
            open(options.lock_ok, "a").close()

        time.sleep(10)

if __name__ ==  "__main__":
    main()