docs: def file_arg(arg):
      """
      Parses a file argument, i.e. starts with file://
      """
      prefix = 'file://'
  
      if arg.startswith(prefix):
          return os.path.abspath(arg[len(prefix):])
      else:
          msg = 'Invalid file argument "{}", does not begin with "file://"'
          raise argparse.ArgumentTypeError(msg.format(arg))