docs: def calculate_width_and_height(url_parts, options):
      '''Appends width and height information to url'''
      width = options.get('width', 0)
      has_width = width
      height = options.get('height', 0)
      has_height = height
  
      flip = options.get('flip', False)
      flop = options.get('flop', False)
  
      if flip:
          width = width * -1
      if flop:
          height = height * -1
  
      if not has_width and not has_height:
          if flip:
              width = "-0"
          if flop:
              height = "-0"
  
      if width or height:
          url_parts.append('%sx%s' % (width, height))