docs: def load(self, txt_fst_file_name):
          """
          Save the transducer in the text file format of OpenFST.
          The format is specified as follows:
              arc format: src dest ilabel olabel [weight]
              final state format: state [weight]
          lines may occur in any order except initial state must be first line
          Args:
              txt_fst_file_name (str): The input file
          Returns:
              None
          """
          with open(txt_fst_file_name, 'r') as input_filename:
              for line in input_filename:
                  line = line.strip()
                  split_line = line.split()
                  if len(split_line) == 1:
                      self[int(split_line[0])].final = True
                  else:
                      self.add_arc(int(split_line[0]), int(split_line[1]),
                                   split_line[2].decode('hex'))