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python-xlib example which reacts to changing the active window
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#!/usr/bin/env python | |
"""python-xlib example which reacts to changing the active window/title. | |
Requires: | |
- Python | |
- python-xlib | |
Tested with Python 2.x because my Kubuntu 14.04 doesn't come with python-xlib | |
for Python 3.x. | |
Design: | |
------- | |
Any modern window manager that isn't horrendously broken maintains an X11 | |
property on the root window named _NET_ACTIVE_WINDOW. | |
Any modern application toolkit presents the window title via a property | |
named _NET_WM_NAME. | |
This listens for changes to both of them and then hides duplicate events | |
so it only reacts to title changes once. | |
""" | |
from contextlib import contextmanager | |
import Xlib | |
import Xlib.display | |
# Connect to the X server and get the root window | |
disp = Xlib.display.Display() | |
root = disp.screen().root | |
# Prepare the property names we use so they can be fed into X11 APIs | |
NET_ACTIVE_WINDOW = disp.intern_atom('_NET_ACTIVE_WINDOW') | |
NET_WM_NAME = disp.intern_atom('_NET_WM_NAME') # UTF-8 | |
WM_NAME = disp.intern_atom('WM_NAME') # Legacy encoding | |
last_seen = { 'xid': None, 'title': None } | |
@contextmanager | |
def window_obj(win_id): | |
"""Simplify dealing with BadWindow (make it either valid or None)""" | |
window_obj = None | |
if win_id: | |
try: | |
window_obj = disp.create_resource_object('window', win_id) | |
except Xlib.error.XError: | |
pass | |
yield window_obj | |
def get_active_window(): | |
"""Return a (window_obj, focus_has_changed) tuple for the active window.""" | |
win_id = root.get_full_property(NET_ACTIVE_WINDOW, | |
Xlib.X.AnyPropertyType).value[0] | |
focus_changed = (win_id != last_seen['xid']) | |
if focus_changed: | |
with window_obj(last_seen['xid']) as old_win: | |
if old_win: | |
old_win.change_attributes(event_mask=Xlib.X.NoEventMask) | |
last_seen['xid'] = win_id | |
with window_obj(win_id) as new_win: | |
if new_win: | |
new_win.change_attributes(event_mask=Xlib.X.PropertyChangeMask) | |
return win_id, focus_changed | |
def _get_window_name_inner(win_obj): | |
"""Simplify dealing with _NET_WM_NAME (UTF-8) vs. WM_NAME (legacy)""" | |
for atom in (NET_WM_NAME, WM_NAME): | |
try: | |
window_name = win_obj.get_full_property(atom, 0) | |
except UnicodeDecodeError: # Apparently a Debian distro package bug | |
title = "<could not decode characters>" | |
else: | |
if window_name: | |
win_name = window_name.value | |
if isinstance(win_name, bytes): | |
# Apparently COMPOUND_TEXT is so arcane that this is how | |
# tools like xprop deal with receiving it these days | |
win_name = win_name.decode('latin1', 'replace') | |
return win_name | |
else: | |
title = "<unnamed window>" | |
return "{} (XID: {})".format(title, win_obj.id) | |
def get_window_name(win_id): | |
"""Look up the window name for a given X11 window ID""" | |
if not win_id: | |
last_seen['title'] = "<no window id>" | |
return last_seen['title'] | |
title_changed = False | |
with window_obj(win_id) as wobj: | |
if wobj: | |
win_title = _get_window_name_inner(wobj) | |
title_changed = (win_title != last_seen['title']) | |
last_seen['title'] = win_title | |
return last_seen['title'], title_changed | |
def handle_xevent(event): | |
# Loop through, ignoring events until we're notified of focus/title change | |
if event.type != Xlib.X.PropertyNotify: | |
return | |
changed = False | |
if event.atom == NET_ACTIVE_WINDOW: | |
if get_active_window()[1]: | |
changed = changed or get_window_name(last_seen['xid'])[1] | |
elif event.atom in (NET_WM_NAME, WM_NAME): | |
changed = changed or get_window_name(last_seen['xid'])[1] | |
if changed: | |
handle_change(last_seen) | |
def handle_change(new_state): | |
"""Replace this with whatever you want to actually do""" | |
print(new_state) | |
if __name__ == '__main__': | |
# Listen for _NET_ACTIVE_WINDOW changes | |
root.change_attributes(event_mask=Xlib.X.PropertyChangeMask) | |
# Prime last_seen with whatever window was active when we started this | |
get_window_name(get_active_window()[0]) | |
handle_change(last_seen) | |
while True: # next_event() sleeps until we get an event | |
handle_xevent(disp.next_event()) |
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