code: def animate(self, sprite, duration = None, easing = None, on_complete = None,
                  on_update = None, round = False, **kwargs):
          
          if not self.tweener: # here we complain
              raise Exception("pytweener was not found. Include it to enable animations")
  
          tween = self.tweener.add_tween(sprite,
                                         duration=duration,
                                         easing=easing,
                                         on_complete=on_complete,
                                         on_update=on_update,
                                         round=round,
                                         **kwargs)
          self.redraw()
          return tween
docs: Interpolate attributes of the given object using the internal tweener
             and redrawing scene after every tweener update.
             Specify the sprite and sprite's attributes that need changing.
             `duration` defaults to 0.4 seconds and `easing` to cubic in-out
             (for others see pytweener.Easing class).
  
             Redraw is requested right after creating the animation.
             Example::
  
               # tween some_sprite to coordinates (50,100) using default duration and easing
               scene.animate(some_sprite, x = 50, y = 100)