        def finalize_hypos(step, bbsz_idx, eos_scores, combined_noisy_channel_eos_scores):
            """
            Finalize the given hypotheses at this step, while keeping the total
            number of finalized hypotheses per sentence <= beam_size.

            Note: the input must be in the desired finalization order, so that
            hypotheses that appear earlier in the input are preferred to those
            that appear later.

            Args:
                step: current time step
                bbsz_idx: A vector of indices in the range [0, bsz*beam_size),
                    indicating which hypotheses to finalize
                eos_scores: A vector of the same size as bbsz_idx containing
                    fw scores for each hypothesis
                combined_noisy_channel_eos_scores: A vector of the same size as bbsz_idx containing
                    combined noisy channel scores for each hypothesis
            """
            assert bbsz_idx.numel() == eos_scores.numel()

            # clone relevant token and attention tensors
            tokens_clone = tokens.index_select(0, bbsz_idx)
            tokens_clone = tokens_clone[:, 1:step + 2]  # skip the first index, which is EOS
            assert not tokens_clone.eq(self.eos).any()
            tokens_clone[:, step] = self.eos
            attn_clone = attn.index_select(0, bbsz_idx)[:, :, 1:step+2] if attn is not None else None

            # compute scores per token position
            pos_scores = scores.index_select(0, bbsz_idx)[:, :step+1]
            pos_scores[:, step] = eos_scores
            # convert from cumulative to per-position scores
            pos_scores[:, 1:] = pos_scores[:, 1:] - pos_scores[:, :-1]

            # normalize sentence-level scores
            if self.normalize_scores:
                combined_noisy_channel_eos_scores /= (step + 1) ** self.len_penalty

            cum_unfin = []
            prev = 0
            for f in finished:
                if f:
                    prev += 1
                else:
                    cum_unfin.append(prev)

            sents_seen = set()
            for i, (idx, score) in enumerate(zip(bbsz_idx.tolist(), combined_noisy_channel_eos_scores.tolist())):
                unfin_idx = idx // beam_size
                sent = unfin_idx + cum_unfin[unfin_idx]

                sents_seen.add((sent, unfin_idx))

                if self.match_source_len and step > src_lengths_no_eos[unfin_idx]:
                    score = -math.inf

                def get_hypo():

                    if attn_clone is not None:
                        # remove padding tokens from attn scores
                        hypo_attn = attn_clone[i][nonpad_idxs[sent]]
                        _, alignment = hypo_attn.max(dim=0)
                    else:
                        hypo_attn = None
                        alignment = None

                    return {
                        'tokens': tokens_clone[i],
                        'score': score,
                        'attention': hypo_attn,  # src_len x tgt_len
                        'alignment': alignment,
                        'positional_scores': pos_scores[i],
                    }

                if len(finalized[sent]) < beam_size:
                    finalized[sent].append(get_hypo())

            newly_finished = []
            for sent, unfin_idx in sents_seen:
                # check termination conditions for this sentence
                if not finished[sent] and is_finished(sent, step, unfin_idx):
                    finished[sent] = True
                    newly_finished.append(unfin_idx)
            return newly_finished
Finalize the given hypotheses at this step, while keeping the total
number of finalized hypotheses per sentence <= beam_size.

Note: the input must be in the desired finalization order, so that
hypotheses that appear earlier in the input are preferred to those
that appear later.

Args:
step: current time step
bbsz_idx: A vector of indices in the range [0, bsz*beam_size),
indicating which hypotheses to finalize
eos_scores: A vector of the same size as bbsz_idx containing
fw scores for each hypothesis
combined_noisy_channel_eos_scores: A vector of the same size as bbsz_idx containing
combined noisy channel scores for each hypothesis
examples/fast_noisy_channel/noisy_channel_sequence_generator.py