code: def store_to_file(self, filename):
      
      with tf.gfile.Open(filename, "w") as f:
        for i in range(len(self._id_to_token)):
          f.write(self._id_to_token[i] + "\n")
docs: Write vocab file to disk.
  
      Vocab files have one token per line. The file ends in a newline. Reserved
      tokens are written to the vocab file as well.
  
      Args:
        filename: Full path of the file to store the vocab to.