Search through all the objects in the world and
        return the first instance whose tag matches the specified string.

def find_obj_by_tag(self, tag):
        """Search through all the objects in the world and
        return the first instance whose tag matches the specified string."""
        for obj in self.__up_objects:
            if obj.tag == tag:
                return obj

        for obj in self.__draw_objects:
            if obj.tag == tag:
                return obj

        return None