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bleu_tool.py
executable file
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/
bleu_tool.py
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# Copyright 2018 The Tensor2Tensor Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Modifications copyright (C) 2018 Texar
# ==============================================================================
"""BLEU metric utililities used for MT eval.
Usage: python bleu_tool.py --translation=my-wmt13.de --reference=wmt13_deen.de
"""
# This also:
# Put compounds in ATAT format (comparable to papers like GNMT, ConvS2S).
# See https://nlp.stanford.edu/projects/nmt/ :
# 'Also, for historical reasons, we split compound words, e.g.,
# "rich-text format" --> rich ##AT##-##AT## text format."'
# BLEU score will be similar to the one obtained using: mteval-v14.pl
# Note:compound splitting is not implemented in this module
from argparse import ArgumentParser
from io import open
import collections
import math
import re
import sys
import unicodedata
# Dependency imports
import numpy as np
import six
# pylint: disable=redefined-builtin
from six.moves import xrange
from six.moves import zip
# pylint: enable=redefined-builtin
def _get_ngrams(segment, max_order):
"""Extracts all n-grams upto a given maximum order from an input segment.
Args:
segment: text segment from which n-grams will be extracted.
max_order: maximum length in tokens of the n-grams returned by this
methods.
Returns:
The Counter containing all n-grams upto max_order in segment
with a count of how many times each n-gram occurred.
"""
ngram_counts = collections.Counter()
for order in xrange(1, max_order + 1):
for i in xrange(0, len(segment) - order + 1):
ngram = tuple(segment[i:i + order])
ngram_counts[ngram] += 1
return ngram_counts
def compute_bleu(reference_corpus,
translation_corpus,
max_order=4,
use_bp=True):
"""Computes BLEU score of translated segments against references.
Args:
reference_corpus: list of references for each translation. Each
reference should be tokenized into a list of tokens.
translation_corpus: list of translations to score. Each translation
should be tokenized into a list of tokens.
max_order: Maximum n-gram order to use when computing BLEU score.
use_bp: boolean, whether to apply brevity penalty.
Returns:
BLEU score.
"""
reference_length = 0
translation_length = 0
bp = 1.0
geo_mean = 0
matches_by_order = [0] * max_order
possible_matches_by_order = [0] * max_order
precisions = []
for (references, translations) in zip(reference_corpus, translation_corpus):
reference_length += len(references)
translation_length += len(translations)
ref_ngram_counts = _get_ngrams(references, max_order)
translation_ngram_counts = _get_ngrams(translations, max_order)
overlap = dict((ngram,
min(count, translation_ngram_counts[ngram]))
for ngram, count in ref_ngram_counts.items())
for ngram in overlap:
matches_by_order[len(ngram) - 1] += overlap[ngram]
for ngram in translation_ngram_counts:
possible_matches_by_order[len(ngram) - 1] += \
translation_ngram_counts[ngram]
precisions = [0] * max_order
smooth = 1.0
for i in xrange(0, max_order):
if possible_matches_by_order[i] > 0:
precisions[i] = matches_by_order[i] / possible_matches_by_order[i]
if matches_by_order[i] > 0:
precisions[i] = matches_by_order[i] / \
possible_matches_by_order[i]
else:
smooth *= 2
precisions[i] = 1.0 / (smooth * possible_matches_by_order[i])
else:
precisions[i] = 0.0
if max(precisions) > 0:
p_log_sum = sum(math.log(p) for p in precisions if p)
geo_mean = math.exp(p_log_sum / max_order)
if use_bp:
ratio = translation_length / reference_length
if ratio <= 0:
bp = 0
elif ratio < 1.0:
bp = math.exp(1 - 1. / ratio)
else:
bp = 1.0
bleu = geo_mean * bp
return np.float32(bleu)
class UnicodeRegex(object):
"""Ad-hoc hack to recognize all punctuation and symbols."""
# pylint:disable=too-few-public-methods
def __init__(self):
punctuation = self.property_chars("P")
self.nondigit_punct_re = re.compile(r"([^\d])([" + punctuation + r"])")
self.punct_nondigit_re = re.compile(r"([" + punctuation + r"])([^\d])")
self.symbol_re = re.compile("([" + self.property_chars("S") + "])")
def property_chars(self, prefix):
# pylint:disable=no-self-use
return "".join(six.unichr(x) for x in range(sys.maxunicode)
if unicodedata.category(
six.unichr(x)).startswith(prefix))
uregex = UnicodeRegex()
def bleu_tokenize(string):
r"""Tokenize a string following the official BLEU implementation.
See https://github.com/moses-smt/mosesdecoder/"
"blob/master/scripts/generic/mteval-v14.pl#L954-L983
In our case, the input string is expected to be just one line
and no HTML entities de-escaping is needed.
So we just tokenize on punctuation and symbols,
except when a punctuation is preceded and followed by a digit
(e.g. a comma/dot as a thousand/decimal separator).
Note that a numer (e.g. a year) followed by a dot at the end of sentence
is NOT tokenized,
i.e. the dot stays with the number because `s/(\p{P})(\P{N})/ $1 $2/g`
does not match this case (unless we add a space after each sentence).
However, this error is already in the original mteval-v14.pl
and we want to be consistent with it.
Args:
string: the input string
Returns:
a list of tokens
"""
string = uregex.nondigit_punct_re.sub(r"\1 \2 ", string)
string = uregex.punct_nondigit_re.sub(r" \1 \2", string)
string = uregex.symbol_re.sub(r" \1 ", string)
return string.split()
def bleu_wrapper(ref_filename, hyp_filename, case_sensitive=False):
"""Compute BLEU for two files (reference and hypothesis translation)."""
ref_lines = open(ref_filename, encoding='utf-8').read().splitlines()
hyp_lines = open(hyp_filename, encoding='utf-8').read().splitlines()
assert len(ref_lines) == len(hyp_lines)
if not case_sensitive:
ref_lines = [x.lower() for x in ref_lines]
hyp_lines = [x.lower() for x in hyp_lines]
ref_tokens = [bleu_tokenize(x) for x in ref_lines]
hyp_tokens = [bleu_tokenize(x) for x in hyp_lines]
return compute_bleu(ref_tokens, hyp_tokens)
if __name__ == "__main__":
parser = ArgumentParser(description='Compute BLEU score. \
Usage: t2t-bleu --translation=my-wmt13.de --reference=wmt13_deen.de')
parser.add_argument('--translation', type=str)
parser.add_argument('--reference', type=str)
args = parser.parse_args()
bleu = 100 * bleu_wrapper(args.reference,
args.translation,
case_sensitive=False)
print("BLEU_uncased = %6.2f" % bleu)
bleu = 100 * bleu_wrapper(args.reference,
args.translation,
case_sensitive=True)
print("BLEU_cased = %6.2f" % bleu)