code: def regular_file() -> Callable:
      
  
      def check_regular_file(value_to_check):
          value_to_check = str(value_to_check)
          if not os.path.isfile(value_to_check):
              raise argparse.ArgumentTypeError("must exist and be a regular file.")
          return value_to_check
  
      return check_regular_file
docs: Returns a method that can be used in argument parsing to check the argument is a regular file or a symbolic link,
      but not, e.g., a process substitution.
  
      :return: A method that can be used as a type in argparse.