#! /usr/bin/env python
import sys
from ctypes import *
Xlib = CDLL("libX11.so.6")
display = Xlib.XOpenDisplay(None)
if display == 0: sys.exit(2)
w = Xlib.XRootWindow(display, c_int(0))
(root_id, child_id) = (c_uint32(), c_uint32())
(root_x, root_y, win_x, win_y) = (c_int(), c_int(), c_int(), c_int())
mask = c_uint()
ret = Xlib.XQueryPointer(display, c_uint32(w), byref(root_id), byref(child_id),
                         byref(root_x), byref(root_y),
                         byref(win_x), byref(win_y), byref(mask))
if ret == 0: sys.exit(1)
print child_id.value

xwininfo -tree -id $(XQueryPointer)

% xwininfo
xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

xwininfo: Window id: 0xa0000d "flask"

...

xdotool getmouselocation --shell | grep WINDOW

sedGetValue='s/.*=(.*)/1/'
windowId=`xdotool getmouselocation --shell 2>/dev/null |grep WINDOW |sed "$sedGetValue"`
echo $windowId

xdotool click 1|xwininfo|grep 'Window id:'

activeWinLine=$(xprop -root | grep "_NET_ACTIVE_WINDOW(WINDOW)")
activeWinId=${activeWinLine:40}

activeWin="$(xprop -root | sed -n 's/^_NET_ACTIVE_WINDOW(WINDOW): window id # //p')"

activeWin="$(xprop -root)"
activeWin="${activeWin#*_NET_ACTIVE_WINDOW(WINDOW):}'
activeWin="${activeWin%%?_NET_*}'
activeWin="${activeWin##* }'

xprop -root 2>/dev/null | sed -n '/^_NET_ACTIVE_WINDOW/ s/.* // p'

from Xlib.display import Display

display = Display()
window = display.screen().root
result = window.query_pointer()

print(result.child.id)