input: def substring_in_order(string: str) -> List[str]:
      """ Generate and return a list of all substrings of the input 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']
      >>> substring_in_order('')
      []
      """
      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