fix bugs and refactor

textattack/shared/attack.py

@@ -1,7 +1,6 @@
 from collections import deque
 
 import lru
-import numpy as np
 
 import textattack
 from textattack.attack_results import (
@@ -29,6 +28,7 @@ class Attack:
         constraints: A list of constraints to add to the attack, defining which perturbations are valid.
         transformation: The transformation applied at each step of the attack.
         search_method: A strategy for exploring the search space of possible perturbations
+        transformation_cache_size (int): the number of items to keep in the transformations cache
         constraint_cache_size (int): the number of items to keep in the constraints cache
     """
 
@@ -38,6 +38,7 @@ class Attack:
         constraints=[],
         transformation=None,
         search_method=None,
+        transformation_cache_size=2 ** 20,
         constraint_cache_size=2 ** 20,
     ):
         """Initialize an attack object.
@@ -74,6 +75,9 @@ class Attack:
             else:
                 self.constraints.append(constraint)
 
+        self.transformation_cache_size = transformation_cache_size
+        self.transformation_cache = lru.LRU(transformation_cache_size)
+
         self.constraint_cache_size = constraint_cache_size
         self.constraints_cache = lru.LRU(constraint_cache_size)
 
@@ -86,6 +90,24 @@ class Attack:
         )
         self.search_method.filter_transformations = self.filter_transformations
 
+    def _get_transformations_uncached(self, current_text, original_text=None, **kwargs):
+        """Applies ``self.transformation`` to ``text``, then filters the list
+        of possible transformations through the applicable constraints.
+
+        Args:
+            current_text: The current ``AttackedText`` on which to perform the transformations.
+            original_text: The original ``AttackedText`` from which the attack started.
+        Returns:
+            A filtered list of transformations where each transformation matches the constraints
+        """
+        transformed_texts = self.transformation(
+            current_text,
+            pre_transformation_constraints=self.pre_transformation_constraints,
+            **kwargs,
+        )
+        self.transformation_cache[current_text] = tuple(transformed_texts)
+        return transformed_texts
+
     def get_transformations(self, current_text, original_text=None, **kwargs):
         """Applies ``self.transformation`` to ``text``, then filters the list
         of possible transformations through the applicable constraints.
@@ -93,8 +115,6 @@ class Attack:
         Args:
             current_text: The current ``AttackedText`` on which to perform the transformations.
             original_text: The original ``AttackedText`` from which the attack started.
-            apply_constraints: Whether or not to apply post-transformation constraints.
-
         Returns:
             A filtered list of transformations where each transformation matches the constraints
         """
@@ -103,13 +123,17 @@ class Attack:
                 "Cannot call `get_transformations` without a transformation."
             )
 
-        transformed_texts = np.array(
-            self.transformation(
-                current_text,
-                pre_transformation_constraints=self.pre_transformation_constraints,
-                **kwargs,
+        if current_text in self.transformation_cache:
+            # promote transformed_text to the top of the LRU cache
+            self.transformation_cache[current_text] = self.transformation_cache[
+                current_text
+            ]
+            transformed_texts = list(self.transformation_cache[current_text])
+        else:
+            transformed_texts = self._get_transformations_uncached(
+                current_text, original_text, **kwargs
             )
-        )
+
         return self.filter_transformations(
             transformed_texts, current_text, original_text
         )