changed check to six string type #375

Author: janvanrijn

openml/datasets/dataset.py

@@ -373,13 +373,17 @@ def get_features_by_type(self, data_type, exclude=None,
         result : list
             a list of indices that have the specified data type
         '''
-        assert data_type in OpenMLDataFeature.LEGAL_DATA_TYPES, "Illegal feature type requested"
+        if data_type not in OpenMLDataFeature.LEGAL_DATA_TYPES:
+            raise TypeError("Illegal feature type requested")
         if self.ignore_attributes is not None:
-            assert type(self.ignore_attributes) is list, "ignore_attributes should be a list"
+            if not isinstance(self.ignore_attributes, list):
+                raise TypeError("ignore_attributes should be a list")
         if self.row_id_attribute is not None:
-            assert type(self.row_id_attribute) is str, "row id attribute should be a str"
+            if not isinstance(self.row_id_attribute, six.string_types):
+                raise TypeError("row id attribute should be a str")
         if exclude is not None:
-            assert type(exclude) is list, "Exclude should be a list"
+            if not isinstance(exclude, list):
+                raise TypeError("Exclude should be a list")
             # assert all(isinstance(elem, str) for elem in exclude), "Exclude should be a list of strings"
         to_exclude = []
         if exclude is not None: