nightmode.py

#!/usr/bin/env python

import dbus
import subprocess
from gi.repository import GLib
from dbus.mainloop.glib import DBusGMainLoop


night_mode = False
backlight_threshold = 0.3
backlight_property = 'BlPct'
themes = {
    'light': 'org.kde.breeze.desktop',
    'dark': 'org.kde.breezedark.desktop'
}


def main():
    DBusGMainLoop(set_as_default=True)
    bus = dbus.SessionBus()
    add_receiver(bus, handle_backlight_change)
    loop = GLib.MainLoop().run()

def set_theme(name):
    subprocess.Popen(['lookandfeeltool', '-a', themes[name]],
    stdout=subprocess.DEVNULL,
    stderr=subprocess.DEVNULL)

def handle_backlight_change(*args):
    global night_mode
    event = args[1]
    if backlight_property not in event:
        return
    current_backlight = event[backlight_property]
    is_night = current_backlight < backlight_threshold
    if is_night and not night_mode:
        set_theme('dark')
    if not is_night and night_mode:
        set_theme('light')
    night_mode = is_night

def add_receiver(bus, handler):
    bus.add_signal_receiver(
    handler,
    'PropertiesChanged',
    'org.freedesktop.DBus.Properties',
    path='/org/clight/clight'
)

if __name__ == "__main__":
    main()