code: def make_input(self,
                     seq_idx: int,
                     word_vec_prev: mx.sym.Symbol,
                     decoder_state: mx.sym.Symbol) -> AttentionInput:
          
          query = decoder_state
          if self._input_previous_word:
              # (batch_size, num_target_embed + rnn_num_hidden)
              query = mx.sym.concat(word_vec_prev, decoder_state, dim=1,
                                    name='%sconcat_prev_word_%d' % (self.prefix, seq_idx))
          return AttentionInput(seq_idx=seq_idx, query=query)
docs: Returns AttentionInput to be fed into the attend callable returned by the on() method.
  
          :param seq_idx: Decoder time step.
          :param word_vec_prev: Embedding of previously predicted ord
          :param decoder_state: Current decoder state
          :return: Attention input.