Fix 1651: make word_vec() return immutable vector

gensim/models/keyedvectors.py

@@ -278,9 +278,12 @@ def word_vec(self, word, use_norm=False):
         """
         if word in self.vocab:
             if use_norm:
-                return self.syn0norm[self.vocab[word].index]
+                result = self.syn0norm[self.vocab[word].index]
             else:
-                return self.syn0[self.vocab[word].index]
+                result = self.syn0[self.vocab[word].index]
+
+            result.setflags(write=False)
+            return result
         else:
             raise KeyError("word '%s' not in vocabulary" % word)
 

gensim/test/test_doc2vec.py

@@ -386,6 +386,12 @@ def test_delete_temporary_training_data(self):
         self.model_sanity(model, keep_training=False)
         self.assertTrue(hasattr(model, 'syn1neg'))
 
+    def test_word_vec(self):
+        model = keyedvectors.KeyedVectors.load_word2vec_format(datapath('word2vec_pre_kv_c'))
+        vector = model['says']
+        with self.assertRaises(ValueError):
+            vector *= 0
+
     @log_capture()
     def testBuildVocabWarning(self, l):
         """Test if logger warning is raised on non-ideal input to a doc2vec model"""