Stop tweening an object, without completing the motion or firing the
        on_complete

def kill_tweens(self, obj = None):
        """Stop tweening an object, without completing the motion or firing the
        on_complete"""
        if obj is not None:
            try:
                del self.current_tweens[obj]
            except:
                pass
        else:
            self.current_tweens = collections.defaultdict(set)