textattack-nlp-transformer/textattack/constraints/overlap/words_perturbed.py

import math
from textattack.constraints import Constraint

class WordsPerturbed(Constraint):
    """ A constraint representing a maximum allowed perturbed words. """
    
    def __init__(self, max_num_words=None, max_percent=None):
        if (max_num_words is None) and (max_percent is None):
            raise ValueError('must set either max perc or max num words')
        if max_percent and not (0 <= max_percent <= 1):
            raise ValueError('max perc must be between 0 and 1')
        self.max_num_words = max_num_words
        self.max_percent = max_percent
    
    def __call__(self, x, x_adv, original_text=None):
        if not original_text:
            raise ValueError('Cannot constraint WordsPerturbed without original_text')
        
        num_words_diff = len(x_adv.all_words_diff(original_text))
        if self.max_percent:
            min_num_words = min(len(x_adv.words), len(original_text.words))
            max_words_perturbed = math.ceil(min_num_words * (self.max_percent))
            max_percent_met = num_words_diff <= max_words_perturbed
        else:
            max_percent_met = True
        if self.max_num_words:
            max_num_words_met = num_words_diff <= self.max_num_words
        else:
            max_num_words_met = True
        
        return max_percent_met and max_num_words_met
        
    def extra_repr_keys(self):
        metric = []
        if self.max_percent is not None:
            metric.append('max_percent')
        if self.max_num_words is not None:
            metric.append('max_num_words')
        return metric