code: def regular_folder() -> Callable:
      
  
      def check_regular_directory(value_to_check):
          value_to_check = str(value_to_check)
          if not os.path.isdir(value_to_check):
              raise argparse.ArgumentTypeError("must be a directory.")
          return value_to_check
  
      return check_regular_directory
docs: Returns a method that can be used in argument parsing to check the argument is a directory.
  
      :return: A method that can be used as a type in argparse.