code: def _list_audio_files(self, root, skip_rows=0):
          
          self.synsets = []
          self.items = []
          if not self._train_csv:
              # The audio files are organized in folder structure with
              # directory name as label and audios in them
              self._folder_structure(root)
          else:
              # train_csv contains mapping between filename and label
              self._csv_labelled_dataset(root, skip_rows=skip_rows)
  
          # Generating the synset.txt file now
          if not os.path.exists("./synset.txt"):
              with open("./synset.txt", "w") as synsets_file:
                  for item in self.synsets:
                      synsets_file.write(item+os.linesep)
              print("Synsets is generated as synset.txt")
          else:
              warnings.warn("Synset file already exists in the current directory! Not generating synset.txt.")
docs: Populates synsets - a map of index to label for the data items.
          Populates the data in the dataset, making tuples of (data, label)