python - glib main loop hangs after Popen -

i'm trying build script logs window title when different window becomes active. have far:

import glib import dbus dbus.mainloop.glib import dbusgmainloop  def notifications(bus, message):     if message.get_member() == "event":         args = message.get_args_list()         if args[0] == "activate":             print "hello world"             activewindow = popen("xdotool getactivewindow getwindowname", stdout=pipe, stderr=pipe);              print activewindow.communicate()    dbusgmainloop(set_as_default=true)  bus = dbus.sessionbus() bus.add_match_string_non_blocking("interface='org.kde.knotify',eavesdrop='true'") bus.add_message_filter(notifications)  mainloop = glib.mainloop() mainloop.run() 

however, apparently wrong popen call, , glib seems swallow error. @ least, on irc channel told me. when remove popen , activewindow.communicate() calls, keeps working , message "hello world!" printed in shell whenever switch new window.

with popen , communicate() calls, script prints single "hello world" , hangs after that.

does know:

• how can proper error message?
• what i'm doing wrong in popen call?

thanks in advance!

i can't comment... haven't imported process module, or members (popen, pipe).