code: def _RawGlobPathSpecWithAlphabeticalSchema(
      file_system, parent_path_spec, segment_format, location, segment_length,
      upper_case=False):
    
    segment_number = 0
    segment_files = []
  
    while True:
      segment_index = segment_number
      segment_letters = []
      while len(segment_letters) < segment_length:
        segment_index, remainder = divmod(segment_index, 26)
        if upper_case:
          segment_letters.append(chr(ord('A') + remainder))
        else:
          segment_letters.append(chr(ord('a') + remainder))
  
      # Reverse the segment letters list to form the extension.
      segment_letters = ''.join(segment_letters[::-1])
      segment_location = segment_format.format(location, segment_letters)
  
      # Note that we don't want to set the keyword arguments when not used
      # because the path specification base class will check for unused
      # keyword arguments and raise.
      kwargs = path_spec_factory.Factory.GetProperties(parent_path_spec)
  
      kwargs['location'] = segment_location
      if parent_path_spec.parent is not None:
        kwargs['parent'] = parent_path_spec.parent
  
      segment_path_spec = path_spec_factory.Factory.NewPathSpec(
          parent_path_spec.type_indicator, **kwargs)
  
      if not file_system.FileEntryExistsByPathSpec(segment_path_spec):
        break
  
      segment_files.append(segment_path_spec)
  
      segment_number += 1
  
    return segment_files
docs: Globs for path specifications according to an alphabetical naming schema.
  
    Args:
      file_system (FileSystem): file system.
      parent_path_spec (PathSpec): parent path specification.
      segment_format (str): naming schema of the segment file location.
      location (str): the base segment file location string.
      segment_length (int): length (number of characters) of the segment
          indicator.
      upper_case (Optional[bool]): True if the segment name is in upper case.
  
    Returns:
      list[PathSpec]: path specifications that match the glob.