//  [python]
def _target_model(config, featurizer_state, targets, n_outputs, train=False, reuse=None, label_encoder=None, **kwargs):
        text_encoder = label_encoder.encoder
        hf_decoder = featurizer_state["decoder"]
        encoder_decoder_mask = tf.sequence_mask(featurizer_state["lengths"], dtype=tf.float32)
        if targets is not None:
            targets, lengths = targets
            padding_mask = tf.sequence_mask(lengths - 1, dtype=tf.float32)
            decoder_out = hf_decoder(
                input_ids=targets[:, :-1], #decoder_input_ids, # cuts final token off internally?
                attention_mask=padding_mask, #decoder_attention_mask,
                encoder_hidden_states=featurizer_state["sequence_features"], #hidden_states,
                encoder_attention_mask=encoder_decoder_mask, #encoder_attention_mask,
                use_cache=False, #use_cache,
                training=train,
            )
            logits = tf.matmul(
                normalize_embeds(
                    decoder_out.last_hidden_state
                ),
                featurizer_state["embedding"].weights,
                transpose_b=True
            )
            logits = tf.compat.v1.Print(logits, [tf.shape(logits), tf.shape(targets[:, 1:]), targets[:, 1:]])
            loss = tf.nn.sparse_softmax_cross_entropy_with_logits(
                logits=logits, labels=targets[:, 1:], 
            )
            loss = loss * padding_mask
            loss = tf.reduce_sum(loss)
            return {
                "logits": logits,
                "losses": loss
            }

        else:
            if config.delim_tokens:
                # Build list of tokens allowed for all examples
                encoded_delim = text_encoder._encode(config.delim_tokens)[0]
                encoded_delim = list(set(flatten(encoded_delim)))
                encoded_delim.append(text_encoder.end_token)
                # Tile encoded delims to be shape [batch_size, num delim]
                encoded_delim = tf.constant(encoded_delim)[None, :]
                encoded_delim = tf.tile(encoded_delim,
                                        (tf.shape(featurizer_state["inputs"])[0], 1))
                # Add delim tokens to all examples
                constraint = tf.concat((featurizer_state["inputs"], encoded_delim), axis=-1)

            def symbols_to_logits_fn(input_symbols, i, state, first=False): #[batch_size, decoded_ids] to [batch_size, vocab_size]
                decoder_output = hf_decoder(
                    input_ids=input_symbols, #decoder_input_ids,
                    encoder_hidden_states=state["encoder_output"], #hidden_states,
                    encoder_attention_mask=state["encoder_decoder_mask"], #encoder_attention_mask,
                    # TODO: reintroduce past_key_values if we ever need to be able to run this quickly.
                    # past_key_values=None if first else state["past_states"], #decoder_past_key_value_states,
                    # Input ids becomes input_ids=input_symbols[:, -1][:, None] when we do.
                    use_cache=True, #use_cache,
                    training=False,
                )
                # HF return objects break unpacking for some reason
                embeds, present_state = decoder_output.last_hidden_state, decoder_output.past_key_values
                logits = tf.matmul(normalize_embeds(embeds[:, -1]), featurizer_state["embedding"].weights, transpose_b=True)

                if config.delim_tokens:
                    batch_indices = tf.range(tf.shape(state["constraint"])[0])[:, None] + \
                            tf.zeros_like(state["constraint"])
                    full_indices = tf.reshape(tf.stack([batch_indices, state["constraint"]], axis=2), [-1,2])
                    mask = tf.scatter_nd(full_indices,
                                        tf.ones((tf.shape(full_indices)[0],)),
                                        shape=tf.shape(logits))
                    # Normalize for the way scatter_nd handles duplicates
                    mask = tf.math.divide_no_nan(mask, mask)
                    logits = logits * mask + ((1 - mask) * -1e5)
                
                state["past_states"] = present_state
                return (logits, state)

            initial_ids = tf.tile(tf.constant([text_encoder.start_token], dtype=tf.int32), [tf.shape(featurizer_state["sequence_features"])[0]])
            batch_size = tf.shape(initial_ids)[0]
            past_states = tuple(
                (
                    tf.zeros((batch_size, hf_decoder.config.num_heads, 0, hf_decoder.config.d_kv)),
                    tf.zeros((batch_size, hf_decoder.config.num_heads, 0, hf_decoder.config.d_kv)),
                    tf.zeros((batch_size, hf_decoder.config.num_heads, 0, hf_decoder.config.d_kv)),
                    tf.zeros((batch_size, hf_decoder.config.num_heads, 0, hf_decoder.config.d_kv)),
                )
            for _ in range(len(hf_decoder.block)))

            states = {
                "encoder_output": featurizer_state["sequence_features"],
                "encoder_decoder_mask": encoder_decoder_mask,
                "past_states": past_states,
            }
            if config.delim_tokens:
                states["constraint"] = constraint
            beams, probs, _ = beam_search(
                symbols_to_logits_fn=symbols_to_logits_fn,
                initial_ids=initial_ids,
                beam_size=config.beam_size,
                decode_length=config.s2s_decoder_max_length,
                vocab_size=hf_decoder.config.vocab_size,
                alpha=config.beam_search_alpha,
                states=states,
                eos_id=text_encoder.end_token,
                stop_early=True,
                use_top_k_with_unique=True,
            )

            best_beams_i = tf.argmax(probs, -1, output_type=tf.int32)
            best_beam = tf.gather_nd(beams, tf.stack([tf.range(tf.shape(beams)[0]), best_beams_i], -1))
            return {
                "logits": best_beam,
                "losses": -1.0
            }