code: def parse_size(size):
          
          if size.startswith('x'):
              return None, int(size.replace('x', ''))
          if 'x' in size:
              return int(size.split('x')[0]), int(size.split('x')[1])
          return int(size), None
docs: Parses size string into a tuple
  
          :param size: String on the form '100', 'x100 or '100x200'
          :return: Tuple of two integers for width and height
          :rtype: tuple