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| """ | |
| Goal Function for Attempts to minimize the BLEU score | |
| ------------------------------------------------------- | |
| """ | |
| import functools | |
| import nltk | |
| import textattack | |
| from .text_to_text_goal_function import TextToTextGoalFunction | |
| class MinimizeBleu(TextToTextGoalFunction): | |
| """Attempts to minimize the BLEU score between the current output | |
| translation and the reference translation. | |
| BLEU score was defined in (BLEU: a Method for Automatic Evaluation of Machine Translation). | |
| `ArxivURL`_ | |
| .. _ArxivURL: https://www.aclweb.org/anthology/P02-1040.pdf | |
| This goal function is defined in (It’s Morphin’ Time! Combating Linguistic Discrimination with Inflectional Perturbations). | |
| `ArxivURL2`_ | |
| .. _ArxivURL2: https://www.aclweb.org/anthology/2020.acl-main.263 | |
| """ | |
| EPS = 1e-10 | |
| def __init__(self, *args, target_bleu=0.0, **kwargs): | |
| self.target_bleu = target_bleu | |
| super().__init__(*args, **kwargs) | |
| def clear_cache(self): | |
| if self.use_cache: | |
| self._call_model_cache.clear() | |
| get_bleu.cache_clear() | |
| def _is_goal_complete(self, model_output, _): | |
| bleu_score = 1.0 - self._get_score(model_output, _) | |
| return bleu_score <= (self.target_bleu + MinimizeBleu.EPS) | |
| def _get_score(self, model_output, _): | |
| model_output_at = textattack.shared.AttackedText(model_output) | |
| ground_truth_at = textattack.shared.AttackedText(self.ground_truth_output) | |
| bleu_score = get_bleu(model_output_at, ground_truth_at) | |
| return 1.0 - bleu_score | |
| def extra_repr_keys(self): | |
| if self.maximizable: | |
| return ["maximizable"] | |
| else: | |
| return ["maximizable", "target_bleu"] | |
| def get_bleu(a, b): | |
| ref = a.words | |
| hyp = b.words | |
| bleu_score = nltk.translate.bleu_score.sentence_bleu([ref], hyp) | |
| return bleu_score | |