def _remove_plot_object_canvas_item(self, plot_object):
        ## XXX stupid goocanvas API forces us to search for the item
        item_to_remove = plot_object.get_canvas_item()
        for i in range(self.get_n_children()):
            item = self.get_child(i)
            if item is item_to_remove:
                self.remove_child(i)
                break
        else:
            raise ValueError