Here is some example code that answers my question:

#!/usr/bin/python

# This is some example code on howto use dbus to detect when the system returns

#+from hibernation or suspend.



import dbus      # for dbus communication (obviously)

import gobject   # main loop

from dbus.mainloop.glib import DBusGMainLoop # integration into the main loop



def handle_resume_callback():

    print "System just resumed from hibernate or suspend"



DBusGMainLoop(set_as_default=True) # integrate into main loob

bus = dbus.SystemBus()             # connect to dbus system wide

bus.add_signal_receiver(           # defince the signal to listen to

    handle_resume_callback,            # name of callback function

    'Resuming',                        # singal name

    'org.freedesktop.UPower',          # interface

    'org.freedesktop.UPower'           # bus name

)



loop = gobject.MainLoop()          # define mainloop

loop.run()                         # run main loop

See the dbus-python tutorial.