code: def rangify(number_list):
      if not number_list:
          return number_list
      ranges = []
      range_start = prev_num = number_list[0]
      for num in number_list[1:]:
          if num != (prev_num + 1):
              ranges.append((range_start, prev_num))
              range_start = num
          prev_num = num
      ranges.append((range_start, prev_num))
      return ranges