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"""
Alzantot Genetic Algorithm
=======================================
(Generating Natural Language Adversarial Examples)
.. warning::
This attack uses a very slow language model. Consider using the ``fast-alzantot``
recipe instead.
"""
from textattack import Attack
from textattack.constraints.grammaticality.language_models import (
Google1BillionWordsLanguageModel,
)
from textattack.constraints.overlap import MaxWordsPerturbed
from textattack.constraints.pre_transformation import (
InputColumnModification,
RepeatModification,
StopwordModification,
)
from textattack.constraints.semantics import WordEmbeddingDistance
from textattack.goal_functions import UntargetedClassification
from textattack.search_methods import AlzantotGeneticAlgorithm
from textattack.transformations import WordSwapEmbedding
from .attack_recipe import AttackRecipe
class GeneticAlgorithmAlzantot2018(AttackRecipe):
"""Alzantot, M., Sharma, Y., Elgohary, A., Ho, B., Srivastava, M.B., &
Chang, K. (2018).
Generating Natural Language Adversarial Examples.
https://arxiv.org/abs/1804.07998
"""
@staticmethod
def build(model_wrapper):
#
# Swap words with their embedding nearest-neighbors.
#
# Embedding: Counter-fitted Paragram Embeddings.
#
# "[We] fix the hyperparameter values to S = 60, N = 8, K = 4, and δ = 0.5"
#
transformation = WordSwapEmbedding(max_candidates=8)
#
# Don't modify the same word twice or stopwords
#
constraints = [RepeatModification(), StopwordModification()]
#
# During entailment, we should only edit the hypothesis - keep the premise
# the same.
#
input_column_modification = InputColumnModification(
["premise", "hypothesis"], {"premise"}
)
constraints.append(input_column_modification)
#
# Maximum words perturbed percentage of 20%
#
constraints.append(MaxWordsPerturbed(max_percent=0.2))
#
# Maximum word embedding euclidean distance of 0.5.
#
constraints.append(
WordEmbeddingDistance(max_mse_dist=0.5, compare_against_original=False)
)
#
# Language Model
#
constraints.append(
Google1BillionWordsLanguageModel(
top_n_per_index=4, compare_against_original=False
)
)
#
# Goal is untargeted classification
#
goal_function = UntargetedClassification(model_wrapper)
#
# Perform word substitution with a genetic algorithm.
#
search_method = AlzantotGeneticAlgorithm(
pop_size=60, max_iters=20, post_crossover_check=False
)
return Attack(goal_function, constraints, transformation, search_method)
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