Python, Emacs Lisp, Common Lisp, and Chicken Scheme implementations of https://wiki.archlinux.org/index.php/Keyboard_backlight for practice

kb-light.el

(defun kb-light (&optional up-down)
  (interactive)
  (require 'dbus)
  (cl-flet ((kb-light-call (method &rest args)
                           (apply #'dbus-call-method
                                  :system
                                  "org.freedesktop.UPower"
                                  "/org/freedesktop/UPower/KbdBacklight"
                                  "org.freedesktop.UPower.KbdBacklight"
                                  method
                                  args)))
    (let* ((maximum (kb-light-call "GetMaxBrightness"))
           (curr (kb-light-call "GetBrightness"))
           (delta (cond ((string= up-down "+") 17)
                        ((string= up-down "-") -17)
                        (t 0)))
           (new (max 0 (+ curr delta))))
      (when (<= 0 new maximum)
        (kb-light-call "SetBrightness" :int32 new))
      (message "Keyboard Brightness: %s" (round (* 100 (/ (float curr) maximum)))))))

kb-light.lisp

;; (ql:quickload :dbus)

(defun kb-light (&optional up-down)
  (dbus:with-open-bus (bus (dbus:system-server-addresses))
    (dbus:with-introspected-object
        (kb-light bus
                  "/org/freedesktop/UPower/KbdBacklight"
                  "org.freedesktop.UPower")
      (let* ((delta (cond ((string= up-down "+") 2)
                          ((string= up-down "-") -2)
                          (t 0)))
             (current (kb-light "org.freedesktop.UPower.KbdBacklight"
                                "GetBrightness"))
             (maximum (kb-light "org.freedesktop.UPower.KbdBacklight"
                                "GetMaxBrightness"))
             (new (max 0 (+ current delta) )))
        (when (<= 0 new maximum)
          (setq current new)
          (kb-light "org.freedesktop.UPower.KbdBacklight"
                    "SetBrightness"
                    current))
        (format t "~a~%" (round (* 100 (float (/ current maximum)))))))))

kb-light.py

#!/usr/bin/python3
# coding: utf-8
# Original source: https://wiki.archlinux.org/index.php/Keyboard_backlight

from sys import argv
import dbus


def kb_light_set(delta):
    bus = dbus.SystemBus()
    kbd_backlight_proxy = bus.get_object('org.freedesktop.UPower', '/org/freedesktop/UPower/KbdBacklight')
    kbd_backlight = dbus.Interface(kbd_backlight_proxy, 'org.freedesktop.UPower.KbdBacklight')

    current = kbd_backlight.GetBrightness()
    maximum = kbd_backlight.GetMaxBrightness()
    new = max(0, current + delta)

    if 0 <= new <= maximum:
        current = new
        kbd_backlight.SetBrightness(current)

    # Return current backlight level percentage
    return 100 * current / maximum

if __name__ == '__main__':
    if len(argv[1:]) == 1:
        if argv[1] == "--up" or argv[1] == "+":
            # ./kb-light.py (+|--up) to increment
            print(kb_light_set(2))
        elif argv[1] == "--down" or argv[1] == "-":
            # ./kb-light.py (-|--down) to decrement
            print(kb_light_set(-2))
        else:
            print("Unknown argument:", argv[1])
    elif len(argv[1:]) == 0:
        print(kb_light_set(0))
    else:
        print("Script takes exactly one argument.", len(argv[1:]), "arguments provided.")

kb-light.scm

#!/usr/local/bin/csi -s

(use dbus)

(: main (-> string))
(define (main)
  (let* ((kb-light (make-context
                    #:bus system-bus
                    #:service 'org.freedesktop.UPower
                    #:interface 'org.freedesktop.UPower.KbdBacklight
                    #:path '/org/freedesktop/UPower/KbdBacklight))
         (argv (command-line-arguments))
         (up-down (when (not (null? argv)) (car argv)))
         (delta (cond ((equal? up-down "+") 17)
                      ((equal? up-down "-") -17)
                      (else 0)))
         (current (car (call kb-light "GetBrightness")))
         (maximum (car (call kb-light "GetMaxBrightness")))
         (new (max 0 (+ current delta))))
    (when (<= 0 new maximum)
      (call kb-light "SetBrightness" new))
    (format #t "~s~%" (inexact->exact
                       (round (* 100 (/ new maximum)))))))

(main)