code: def parse_size(image, size):
          
          bits = size.split("x")
          if image.size[0] == 0 or image.size[1] == 0:
              ratio = 1.0
          else:
              ratio = float(image.size[0]) / float(image.size[1])
  
          if len(bits) == 1 or not bits[1]:
              width = int(bits[0])
              height = int(1 / ratio * width)
          elif not bits[0]:
              height = int(bits[1])
              width = int(height * ratio)
          else:
              width, height = map(int, bits)
          return width, height
docs: Parse a size string (i.e. "200", "200x100", "x200", etc.) into a
          (width, height) tuple.