PyGObject support for Gtk+2 is rater limited as Gtk+2 wasn't created with full Introspection support.
If you're using PyGobject don't use PyGtk, they are different things. In any case, why you need to use libglade? To support old Software? If that's the case, don't use PyGObject, use whatever version the Software was made with.
If you need to parse Glade files to build a GUI, use Gtk+ included GtkBuilder object, libglade was deprecated long long long long ago.
See gi.repository Windows, in particular differences with Gtk+2 and Gtk+3. Also, see How can a program that uses GUI be constructed? for how to build a Glade GUI using PyGObject, Python2.7 and GtkBuilder (this is what I suppose you need).