| """ | |
| Edit Distance Constraints | |
| -------------------------- | |
| """ | |
| import editdistance | |
| from textattack.constraints import Constraint | |
| class LevenshteinEditDistance(Constraint): | |
| """A constraint on edit distance (Levenshtein Distance). | |
| Args: | |
| max_edit_distance (int): Maximum edit distance allowed. | |
| compare_against_original (bool): If `True`, compare new `x_adv` against the original `x`. | |
| Otherwise, compare it against the previous `x_adv`. | |
| """ | |
| def __init__(self, max_edit_distance, compare_against_original=True): | |
| super().__init__(compare_against_original) | |
| if not isinstance(max_edit_distance, int): | |
| raise TypeError("max_edit_distance must be an int") | |
| self.max_edit_distance = max_edit_distance | |
| def _check_constraint(self, transformed_text, reference_text): | |
| edit_distance = editdistance.eval(reference_text.text, transformed_text.text) | |
| return edit_distance <= self.max_edit_distance | |
| def extra_repr_keys(self): | |
| return ["max_edit_distance"] + super().extra_repr_keys() | |