code: def set_and_check_directories(self, tgt_dir: Path) -> None:
          
          logger.info("Setting up directories for corpus in %s", tgt_dir)
  
          # Check directories exist.
          if not tgt_dir.is_dir():
              raise FileNotFoundError(
                  "The directory {} does not exist.".format(tgt_dir))
          if not self.wav_dir.is_dir():
              raise PersephoneException(
                  "The supplied path requires a 'wav' subdirectory.")
          self.feat_dir.mkdir(parents=True, exist_ok=True)
          if not self.label_dir.is_dir():
              raise PersephoneException(
                  "The supplied path requires a 'label' subdirectory.")
docs: Make sure that the required directories exist in the target directory.
          set variables accordingly.