def replace_oovs(source_in, target_in, target_out):
    """Replaces <unk-N> tokens in the target text with the corresponding word in
    the source text.
    """

    oov_re = re.compile("^<unk-([0-9]+)>$")

    for source_seq, target_seq in zip(source_in, target_in):
        target_seq_out = []

        pos_to_word = source_seq.strip().split()
        for token in target_seq.strip().split():
            m = oov_re.match(token)
            if m:
                pos = int(m.group(1))
                if pos >= len(pos_to_word):
                    raise OOVIndexError(pos, source_seq, target_seq)
                token_out = pos_to_word[pos]
            else:
                token_out = token
            target_seq_out.append(token_out)
        target_out.write(" ".join(target_seq_out) + "\n")
Replaces <unk-N> tokens in the target text with the corresponding word in
    the source text.
    
understand_icl/fairseq/examples/pointer_generator/postprocess.py