python wnck not returning any data until after a pdb.set_trace()

Question

On Ubuntu Linux / Gnome, I am trying to use python's wnck binding to get a list of all the open windows.

My code looks like this:

#! /usr/bin/python

from pprint import pprint
import wnck

screen = wnck.screen_get_default()

pprint(screen.get_windows())

import pdb ; pdb.set_trace()

pprint(screen.get_windows())

The output is like this:

** (windowlist.py:4501): WARNING **: Trying to register gtype 'WnckWindowState' as enum when in fact it is of type 'GFlags'

** (windowlist.py:4501): WARNING **: Trying to register gtype 'WnckWindowActions' as enum when in fact it is of type 'GFlags'

** (windowlist.py:4501): WARNING **: Trying to register gtype 'WnckWindowMoveResizeMask' as enum when in fact it is of type 'GFlags'
[]
> /home/rory/personal/diriu/windowlist.py(12)<module>()
-> pprint(screen.get_windows())
(Pdb) c
[<wnck.Window object at 0xb61db0cc (WnckWindow at 0x992c000)>,
 <wnck.Window object at 0xb61db0f4 (WnckWindow at 0x992c0a8)>,
 <wnck.Window object at 0xb61db11c (WnckWindow at 0x992c150)>,
 <wnck.Window object at 0xb61db144 (WnckWindow at 0x992c1f8)>,
 <wnck.Window object at 0xb61db16c (WnckWindow at 0x992c2a0)>,
 <wnck.Window object at 0xb61db194 (WnckWindow at 0x992c348)>,
 <wnck.Window object at 0xb61db1bc (WnckWindow at 0x992c3f0)>,
 <wnck.Window object at 0xb61db1e4 (WnckWindow at 0x992c498)>,
 <wnck.Window object at 0xb61db20c (WnckWindow at 0x992c540)>,
 <wnck.Window object at 0xb61db234 (WnckWindow at 0x992c5e8)>,
 <wnck.Window object at 0xb61db25c (WnckWindow at 0x992c690)>,
 <wnck.Window object at 0xb61db284 (WnckWindow at 0x992c738)>]

The first get_windows() call returns [], an empty list. The second get_windows() call returns a list of open windows. In the pdb, I only press c to continue and do nothing (in pdb).

If I comment out the pdb, the both get_windows() calls return []. If I repeat the get_windows() call many time before the pdb, there is nothing. If I repeat the get_windows() call many times after the pdb, i continually get a full list.

Why is this call only working after an empty pdb? How do I make it work without a pdb?

Answer 1

File so-wnck.py (from How might I grab all windows with a certain word in their titles?)

import pygtk
pygtk.require('2.0')
import gtk
import wnck

screen = wnck.screen_get_default()
while gtk.events_pending():
    gtk.main_iteration()

windows = screen.get_windows()
print (windows)

python so-wnck.py

** (so-wnck.py:2367): WARNING **: Trying to register gtype 'WnckWindowState' as enum when in fact it is of type 'GFlags'

** (so-wnck.py:2367): WARNING **: Trying to register gtype 'WnckWindowActions' as enum when in fact it is of type 'GFlags'

** (so-wnck.py:2367): WARNING **: Trying to register gtype 'WnckWindowMoveResizeMask' as enum when in fact it is of type 'GFlags'
[<wnck.Window object at 0xb7566694 (WnckWindow at 0x97c51f8)>,
 <wnck.Window object at 0xb75666bc (WnckWindow at 0x97c52a0)>, 
 <wnck.Window object at 0xb75666e4 (WnckWindow at 0x97c5348)>, 
 <wnck.Window object at 0xb756670c (WnckWindow at 0x97c53f0)>, 
 <wnck.Window object at 0xb7566734 (WnckWindow at 0x97c5498)>,
 <wnck.Window object at 0xb756675c (WnckWindow at 0x97c5540)>, 
 <wnck.Window object at 0xb7566784 (WnckWindow at 0x97c55e8)>]

Answer 2

I doesn't work with wnck but I think that in case with pdb time between two calls to get_window enough to windows list initialized. Try to use sleep with some delay before call to get_window.