add kuleshov recipe; rename attack_methods --> search_methods

textattack/constraints/grammaticality/language_models/language_model_constraint.py

@@ -0,0 +1,40 @@
+import math
+import torch
+
+from textattack.constraints import Constraint
+
+class LanguageModelConstraint(Constraint):
+    """ 
+        Determines if two sentences have a swapped word that has a similar
+            probability according to a language model.
+        
+        Args:
+            max_log_prob_diff (float): the maximum difference in log-probability
+                between x and x_adv
+    """
+    
+    def __init__(self, max_log_prob_diff=None):
+        if max_log_prob_diff is None:
+            raise ValueError('Must set max_log_prob_diff')
+        self.max_log_prob_diff = max_log_prob_diff
+    
+    def get_log_prob_at_index(self, text_list, word_index):
+        """ Gets the log-probability of `text` at index `word_index` according 
+        to a language model.
+        """
+        raise NotImplementedError()
+    
+    def __call__(self, x, x_adv, original_text=None):
+        try:
+            i = x_adv.attack_attrs['modified_word_index']
+        except AttributeError:
+            raise AttributeError('Cannot apply language model constraint without `modified_word_index`')
+            
+        x_prob = self.get_log_prob_at_index(x, i)
+        x_adv_prob = self.get_log_prob_at_index(x_adv, i)
+        if self.max_log_prob_diff is None:
+            x_prob, x_adv_prob = math.log(p1), math.log(p2)
+        return (x_prob - x_adv_prob).abs() <= self.max_log_prob_diff
+    
+    def extra_repr_keys(self):
+        return ['max_log_prob_diff']