code: def sprite(map, sprite, offset_x=None, offset_y=None, cache_buster=True):
      
      map = map.render()
      sprite_maps = _get_cache('sprite_maps')
      sprite_map = sprite_maps.get(map)
      sprite_name = String.unquoted(sprite).value
      sprite = sprite_map and sprite_map.get(sprite_name)
      if not sprite_map:
          log.error("No sprite map found: %s", map, extra={'stack': True})
      elif not sprite:
          log.error("No sprite found: %s in %s", sprite_name, sprite_map['*n*'], extra={'stack': True})
      if sprite:
          url = '%s%s' % (config.ASSETS_URL, sprite_map['*f*'])
          if cache_buster:
              url += '?_=%s' % sprite_map['*t*']
          x = Number(offset_x or 0, 'px')
          y = Number(offset_y or 0, 'px')
          if not x.value or (x.value <= -1 or x.value >= 1) and not x.is_simple_unit('%'):
              x -= Number(sprite[2], 'px')
          if not y.value or (y.value <= -1 or y.value >= 1) and not y.is_simple_unit('%'):
              y -= Number(sprite[3], 'px')
          url = "url(%s)" % escape(url)
          return List([String.unquoted(url), x, y])
      return List([Number(0), Number(0)])
docs: Returns the image and background position for use in a single shorthand
      property