Look at the example in the bottom of this page: http://www.pygtk.org/pygtk2tutorial/sec-EventHandling.html it says:
57 def button_press_event(widget, event):
58 if event.button == 1 and pixmap != None:
59 draw_brush(widget, event.x, event.y)
60 return True
So, for what there are "return True"?