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PaddleSpeech/deepspeech/decoders/ctcdecoder/scorer_deprecated.py

79 lines
2.7 KiB

# Copyright (c) 2021 PaddlePaddle Authors. All Rights Reserved.
#
# 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.
"""External Scorer for Beam Search Decoder."""
import os
import kenlm
import numpy as np
class Scorer(object):
"""External scorer to evaluate a prefix or whole sentence in
beam search decoding, including the score from n-gram language
model and word count.
:param alpha: Parameter associated with language model. Don't use
language model when alpha = 0.
:type alpha: float
:param beta: Parameter associated with word count. Don't use word
count when beta = 0.
:type beta: float
:model_path: Path to load language model.
:type model_path: str
"""
def __init__(self, alpha, beta, model_path):
self._alpha = alpha
self._beta = beta
if not os.path.isfile(model_path):
raise IOError("Invaid language model path: %s" % model_path)
self._language_model = kenlm.LanguageModel(model_path)
# n-gram language model scoring
def _language_model_score(self, sentence):
#log10 prob of last word
log_cond_prob = list(
self._language_model.full_scores(sentence, eos=False))[-1][0]
return np.power(10, log_cond_prob)
# word insertion term
def _word_count(self, sentence):
words = sentence.strip().split(' ')
return len(words)
# reset alpha and beta
def reset_params(self, alpha, beta):
self._alpha = alpha
self._beta = beta
# execute evaluation
def __call__(self, sentence, log=False):
"""Evaluation function, gathering all the different scores
and return the final one.
:param sentence: The input sentence for evalutation
:type sentence: str
:param log: Whether return the score in log representation.
:type log: bool
:return: Evaluation score, in the decimal or log.
:rtype: float
"""
lm = self._language_model_score(sentence)
word_cnt = self._word_count(sentence)
if log is False:
score = np.power(lm, self._alpha) * np.power(word_cnt, self._beta)
else:
score = self._alpha * np.log(lm) + self._beta * np.log(word_cnt)
return score