code: def _sprite(map, sprite, offset_x=None, offset_y=None):
      
      map = StringValue(map).value
      sprite_name = StringValue(sprite).value
      sprite_map = sprite_maps.get(map)
      sprite = sprite_map and sprite_map.get(sprite_name)
      if not sprite_map:
          log.error("No sprite map found: %s", map)
      elif not sprite:
          log.error("No sprite found: %s in %s", sprite_name, sprite_map['*n*'])
      if sprite:
          url = '%s%s?_=%s' % (ASSETS_URL, sprite_map['*f*'], sprite_map['*t*'])
          x = NumberValue(offset_x or 0, 'px')
          y = NumberValue(offset_y or 0, 'px')
          if not x or (x <= -1 or x >= 1) and x.unit != '%':
              x -= sprite[2]
          if not y or (y <= -1 or y >= 1) and y.unit != '%':
              y -= sprite[3]
          pos = "url(%s) %s %s" % (escape(url), x, y)
          return StringValue(pos)
      return StringValue('0 0')
docs: Returns the image and background position for use in a single shorthand
      property