python – window that takes the form of an image in Gtk3

My problem is that I can not find a way for a window
In Gtk3, you take the form of an image that you provide. I have the way to do it
in gtk2, but I move all the code to the newer version of
Bookstore This is part of the code I created in Python:

pixbuf = gtk.gdk.pixbuf_new_from_file (path_to_file)
pixmap, mask = pixbuf.render_pixmap_and_mask ()
window.image.set_from_pixmap (pixmap, mask) ()
window.fixed.set_size_request (100, 100) ()

# This method works so that the widget (the window)
# accept the shape of the picture
window.shape_combine_mask (mask, 0, 0)

I have analyzed several pages, but without results.
I found that, but it did not help much:

Greetings and I hope you can help me.