fix defaultdict call

JelleZijlstra · JelleZijlstra · commit fe6b9ea1a027 · 2014-06-03T19:34:41.000-07:00
In Python 2.7, the current version fails with:

$ python -c 'from collections import defaultdict; defaultdict(None)'
Traceback (most recent call last):
  File "&lt;string&gt;", line 1, in &lt;module&gt;
TypeError: first argument must be callable
diff --git a/sklearn/feature_extraction/text.py b/sklearn/feature_extraction/text.py
@@ -726,7 +726,7 @@ def _count_vocab(self, raw_documents, fixed_vocab):
             vocabulary = self.vocabulary_
         else:
             # Add a new value when a new vocabulary item is seen
-            vocabulary = defaultdict(None)
+            vocabulary = defaultdict()
             vocabulary.default_factory = vocabulary.__len__
 
         analyze = self.build_analyzer()
