input: 
  def substring_in_order(string: str) -> List[str]:
      """ Generate all substrings of a given string in order from longest to shortest length.
      >>> substring_in_order("abc")
      ['abc', 'ab', 'bc', 'a', 'b', 'c']
      >>> substring_in_order("xyz")
      ['xyz', 'xy', 'yz', 'x', 'y', 'z']
      """
      result = []
      n = len(string)
      for l in range(n, 0, -1):
          for i in range(n-l + 1):
              result.append(string[i:i+l])
      return result
  
output:     result = []
      n = len(string)
      for l in range(n, 0, -1):
          for i in range(n-l + 1):
              result.append(string[i:i+l])
      return result