#!/usr/bin/python
import dbus
bus = dbus.Bus(dbus.Bus.TYPE_SESSION)
devobj = bus.get_object('org.gnome.PowerManager', '/org/gnome/PowerManager')
dev = dbus.Interface(devobj, "org.gnome.PowerManager")
cookie = dev.Inhibit('Nautilus', 'Copying files')
#do something 
dev.UnInhibit(cookie)