[6.1] AC invalid k for predict_topk. (#2856)

Author: jakesabathia2

src/python/turicreate/test/test_activity_classifier.py

@@ -439,6 +439,18 @@ def test_predict_topk(self):
             expected_len = self._calc_expected_predictions_length(self.data.head(100), top_k=5)
             self.assertEqual(len(preds), expected_len)
 
+    def test_predict_topk_invalid_k(self):
+        model = self.model
+        with self.assertRaises(_ToolkitError):
+            preds = model.predict_topk(self.data, k=-1)
+
+        with self.assertRaises(_ToolkitError):
+            preds = model.predict_topk(self.data, k=0)
+
+        with self.assertRaises(TypeError):
+            preds = model.predict_topk(self.data, k=[])
+
+
     def test_evaluate_with_incomplete_targets(self):
         """
         Check that evaluation does not require the test data to span all labels.

src/python/turicreate/toolkits/activity_classifier/_activity_classifier.py

@@ -611,6 +611,9 @@ def predict_topk(self, dataset, output_type='probability', k=3, output_frequency
         |      ...      |  ...  |        ...        |
         +---------------+-------+-------------------+
         """
+        if not isinstance(k, int):
+            raise TypeError('k must be of type int')
+        _tkutl._numeric_param_check_range('k', k, 1, _six.MAXSIZE)
         return self.__proxy__.predict_topk(dataset, output_type, k, output_frequency);
 
     def classify(self, dataset, output_frequency='per_row'):