"""
Word Swap
-------------------------------
Word swap transformations act by replacing some words in the input. Subclasses can implement the abstract ``WordSwap`` class by overriding ``self._get_replacement_words``
"""
import random
import string
from textattack.transformations import Transformation
[docs]class WordSwap(Transformation):
"""An abstract class that takes a sentence and transforms it by replacing
some of its words.
letters_to_insert (string): letters allowed for insertion into words
(used by some char-based transformations)
"""
def __init__(self, letters_to_insert=None):
self.letters_to_insert = letters_to_insert
if not self.letters_to_insert:
self.letters_to_insert = string.ascii_letters
def _get_replacement_words(self, word):
"""Returns a set of replacements given an input word. Must be overriden
by specific word swap transformations.
Args:
word: The input word to find replacements for.
"""
raise NotImplementedError()
def _get_random_letter(self):
"""Helper function that returns a random single letter from the English
alphabet that could be lowercase or uppercase."""
return random.choice(self.letters_to_insert)
def _get_transformations(self, current_text, indices_to_modify):
words = current_text.words
transformed_texts = []
for i in indices_to_modify:
word_to_replace = words[i]
replacement_words = self._get_replacement_words(word_to_replace)
transformed_texts_idx = []
for r in replacement_words:
if r == word_to_replace:
continue
transformed_texts_idx.append(current_text.replace_word_at_index(i, r))
transformed_texts.extend(transformed_texts_idx)
return transformed_texts