ContextIndex now pays attention to a user-supplied context_func

nltk/text.py

@@ -45,7 +45,9 @@ class ContextIndex(object):
     def __init__(self, tokens, context_func=None, filter=None, key=lambda x:x):
         self._key = key
         self._tokens = tokens
-        if not context_func:
+        if context_func:
+            self._context_func = context_func
+        else:
             self._context_func = self._default_context
         if filter:
             tokens = [t for t in tokens if filter(t)]