about widget creation in libglade

Hi,

I have one doubt regarding libglade.  How is it
creating the widgets from glade file.  It seems like
the widgets are created during creation of GladeXML
object.
  gxml = glade.XML('pathtogladefile')

I am searching for a way to _apply_ glade file to
existing widget (which is already created).  

I will make the above point clearer.  Look at the
following pygtk example, which doesn't use libglade.

class MyWindow(gtk.Window):
    def __init__(self):
        super(MyWindow, self).__init__()
        # any other stuffs like adding widgets
win = MyWindow()
win.show()

The main advantage of this style is `win` is actually
_is_ a widget (a gtk.Window).  So I call win.show()
instead of doing tricks like win.widget.show().  But
is it possible to achieve this advantage, when using
glade file for generating the UI.  NO!  I tried the
following.

class MyWindow2(gtk.Window):
    def __init__(self):