Fix Issue #743, Updated word2vec.n_similarities and test_word2vec.testSimilarities methods

CHANGELOG.md

@@ -1,6 +1,9 @@
 Changes
 =======
 
+0.13.3, 2016-09-26
+* Fixed issue #743 , In word2vec's n_similarity method if atleast one empty list is passed ZeroDivisionError is raised, added test cases in test/test_word2vec.py(@pranay360, #883)
+
 0.13.2, 2016-08-19
 * export_phrases in Phrases model changed. Fixed issue #794 and added test cases in test/test_phrases.py(@AadityaJ,
 [#879](https://github.com/RaRe-Technologies/gensim/pull/879))

gensim/models/word2vec.py

@@ -1539,9 +1539,13 @@ def n_similarity(self, ws1, ws2):
           True
 
         """
+        if not(len(ws1) and len(ws2)):
+            raise ZeroDivisionError('Atleast one of the passed list is empty.')
         v1 = [self[word] for word in ws1]
         v2 = [self[word] for word in ws2]
-        return dot(matutils.unitvec(array(v1).mean(axis=0)), matutils.unitvec(array(v2).mean(axis=0)))
+        return dot(matutils.unitvec(array(v1).mean(axis=0)),
+                   matutils.unitvec(array(v2).mean(axis=0)))
+
 
     def init_sims(self, replace=False):
         """

gensim/test/test_word2vec.py

@@ -370,9 +370,12 @@ def testSimilarities(self):
         model = word2vec.Word2Vec(size=2, min_count=1, sg=0, hs=0, negative=2)
         model.build_vocab(sentences)
         model.train(sentences)
-
+        
         self.assertTrue(model.n_similarity(['graph', 'trees'], ['trees', 'graph']))
         self.assertTrue(model.n_similarity(['graph'], ['trees']) == model.similarity('graph', 'trees'))
+        self.assertRaises(ZeroDivisionError, model.n_similarity, ['graph', 'trees'], [])
+        self.assertRaises(ZeroDivisionError, model.n_similarity, [], ['graph', 'trees'])
+        self.assertRaises(ZeroDivisionError, model.n_similarity, [], [])
 
     def testSimilarBy(self):
         """Test word2vec similar_by_word and similar_by_vector."""