Getting notified about window title changes
Well, thanks to @Basile's comment, I learned a lot and came up with following working sample:
#!/usr/bin/python3
import Xlib
import Xlib.display
disp = Xlib.display.Display()
root = disp.screen().root
NET_WM_NAME = disp.intern_atom('_NET_WM_NAME')
NET_ACTIVE_WINDOW = disp.intern_atom('_NET_ACTIVE_WINDOW')
root.change_attributes(event_mask=Xlib.X.FocusChangeMask)
while True:
try:
window_id = root.get_full_property(NET_ACTIVE_WINDOW, Xlib.X.AnyPropertyType).value[0]
window = disp.create_resource_object('window', window_id)
window.change_attributes(event_mask=Xlib.X.PropertyChangeMask)
window_name = window.get_full_property(NET_WM_NAME, 0).value
except Xlib.error.XError:
window_name = None
print(window_name)
event = disp.next_event()
Rather than running xdotool
naively, it listens synchronously to events generated by X which is exactly what I was after.
I couldn't get your focus-change approach to work reliably under Kwin 4.x, but modern window managers maintain a _NET_ACTIVE_WINDOW
property on the root window that you can listen for changes to.
Here's a Python implementation of just that:
#!/usr/bin/python
from contextlib import contextmanager
import Xlib
import Xlib.display
disp = Xlib.display.Display()
root = disp.screen().root
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():
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):
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):
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__':
root.change_attributes(event_mask=Xlib.X.PropertyChangeMask)
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())
The more fully-commented version I wrote as an example for someone is in this gist.
UPDATE: Now, it also demonstrates the second half (listening to _NET_WM_NAME
) to do exactly what was requested.
UPDATE #2: ...and the third part: Falling back to WM_NAME
if something like xterm hasn't set _NET_WM_NAME
. (The latter is UTF-8 encoded while the former is supposed to use a legacy character coding called compound text but, since nobody seems to know how to work with it, you get programs throwing whatever stream of bytes they have in there and xprop
just assuming it'll be ISO-8859-1.)