Bleu.py 文件源码

def _compute_bleu(p, len_pred, len_gold, smooth):
    # Brevity penalty.
    log_brevity = 1 - max(1, (len_gold + smooth) / (len_pred + smooth))
    log_score = 0
    ngrams = len(p) - 1
    for n in range(1, ngrams + 1):
        if p[n][1] > 0:
            if p[n][0] == 0:
                p[n][0] = 1e-16
            log_precision = math.log((p[n][0] + smooth) / (p[n][1] + smooth))
            log_score += log_precision
    log_score /= ngrams
    return math.exp(log_score + log_brevity)


# Calculate BLEU of prefixes of pred.