"""
chrF Constraints
--------------------------
"""
import nltk.translate.chrf_score
from textattack.constraints import Constraint
[docs]class chrF(Constraint):
"""A constraint on chrF (n-gram F-score) difference.
Args:
max_chrf (int): Max n-gram F-score 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_chrf, compare_against_original=True):
super().__init__(compare_against_original)
if not isinstance(max_chrf, int):
raise TypeError("max_chrf must be an int")
self.max_chrf = max_chrf
def _check_constraint(self, transformed_text, reference_text):
ref = reference_text.words
hyp = transformed_text.words
chrf = nltk.translate.chrf_score.sentence_chrf(ref, hyp)
return chrf <= self.max_chrf