Pygtk - How to center a window on a parent window border?

How can I make a child widget (in this case other window, a popup one) popup attached to the border of the parent window? I know I can center it in the parent with: gtk.Window.set_position(g开发者_C百科tk.WIN_POS_CENTER_ON_PARENT), but how can I make it popup in the border?

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Solved...:P

I managed to solve it by using:

(x, y) = parent.get_position()

y1 = y+50

child.move(x, y1)