code: def rename_file_group_to_serial_nums(file_lst):
      
      file_lst.sort()
      c = 1
      for f in file_lst:
          dirname = get_abspath(f.dirname())
          fdest = f.joinpath(dirname, "{0:04d}".format(c) +
                             OUTPUT_DICOM_EXTENSION)
          log.info('Renaming {0} to {1}'.format(f, fdest))
          f.rename(fdest)
          c += 1
docs: Will rename all files in file_lst to a padded serial
      number plus its extension
  
      :param file_lst: list of path.py paths