Toggles Enabled/Disabled state of X11 input devices

#!/usr/bin/env python
# x11devprop.py
"""
    (C) 2014 G. Bege <therion@ninth-art.de>
    Created on: 02nd June 2014
    Modified on:    03rd June 2014
    Licensed under the GPLv3 <http://www.gnu.org/licenses/gpl-3.0.html>

    Description
    -------------------
    This script calls the X11 API in order to change
    an input device property.
    However its only as much implemented as necessary
    in order to enable/disable a device.

    Dependencies
    ------------------------
    X Input 1.5 required

    Note
    --------
    Tested against Xorg 7.4 @ Gentoo
    For device ID's use xinput
"""
import atexit
from sys import exit, argv
from ctypes import *
cdll.LoadLibrary("libX11.so.6") # XopenDisplay, XCloseDisplay, XInternAtom
cdll.LoadLibrary("libXi.so.6")  # XOpenDevice, XCloseDevice
                # XiGetDeviceProperty, XiSetDeviceProperty
libx11 = CDLL("libX11.so.6")
libxi = CDLL("libXi.so.6")
Display = Device = 0x0
Options = ("Enable", "Disable", "Toggle")
Version = 0.112

Success = 0             # <X11/X.h>
PropModeReplace = 0         # <X11/X.h>
AnyPropertyType = c_long(0)     # <X11/X.h>

# Atom defined as CARD32        <X11/X.h>
# CARD32 defined as unsigned int    <X11/Xmd.h>
def Atom(I):
    return c_uint(I)

def Cleanup():
    global Display, Device
    if Device != 0x0:   libxi.XCloseDevice(Display, Device);
    if Display != 0x0:  libx11.XCloseDisplay(Display);
atexit.register(Cleanup)

# @description      Invokes X11 device with "Device Enabled" Atom
# @param    devid   device id
# @param    value   property value
# @note     this function accepts a toggle value 0xff
def X11DeviceEnable(devid, value):
    global Display, Device
    assert isinstance(devid, int)

    Display = libx11.XOpenDisplay(None)
    if Display == 0x0:
        print "Error: Unable to open X11 display."
        exit(1)

    Device = libxi.XOpenDevice(Display, c_uint(devid))
    if Device == 0x0:
        print "Error: Unable to open device (%d)." % devid
        exit(1)

    # retrieve current device properties
    prop = libx11.XInternAtom(Display, "Device Enabled", False)
    type = Atom(0)
    format = c_int(0)
    act_nitems = bytes_after = c_ulong(0)
    data = c_int(0)
    ret = libxi.XGetDeviceProperty(Display, Device, prop, 0, 1, False, AnyPropertyType,
            byref(type), byref(format), byref(act_nitems),
            byref(bytes_after), byref(data));
    if ret != Success:
        print "Failed to get property type and format for Deviceice (%d)." % devid
        exit(1)
    curstate = c_byte.from_address(data.value)

    # Note: we only support a single value
    assert isinstance(value, int)
    nelem = 1
    data = (c_int*nelem)()

    # 0xff will act like a switch on the state
    if value == 0xff:
        if curstate.value == 1: data[0] = 0;
        else:           data[0] = 1;
    else:
        data[0] = value

    ret = libxi.XChangeDeviceProperty(Display, Device, prop, type,  format,
                        PropModeReplace, data, nelem);
    if ret != Success:
        print "Failed to set property:%c, type:%d, format:%d on device %d." % (prop, type, format, devid)
        exit(1)

if __name__ == '__main__':
    if len(argv) < 3 or argv[2] not in Options:
        exit('Usage: %s <devid> (Enable|Disable|Toggle)' % argv[0])
    devid = int(argv[1])

    if argv[2] == "Enable":     X11DeviceEnable(devid, 0x1);
    elif argv[2] == "Toggle":   X11DeviceEnable(devid, 0xff);
    else:               X11DeviceEnable(devid, 0x0);

exit(0)