make sure repr workes with blank / fresh datasets (#820)

* make sure repr workes with blank / fresh datasets

* PEP8

Author: amueller

openml/datasets/dataset.py

@@ -184,12 +184,13 @@ def __repr__(self):
                   "Download URL": self.url,
                   "Data file": self.data_file,
                   "Pickle file": self.data_pickle_file,
-                  "# of features": len(self.features)}
+                  "# of features": len(self.features)
+                  if self.features is not None else None}
         if self.upload_date is not None:
             fields["Upload Date"] = self.upload_date.replace('T', ' ')
         if self.dataset_id is not None:
             fields["OpenML URL"] = "{}d/{}".format(base_url, self.dataset_id)
-        if self.qualities['NumberOfInstances'] is not None:
+        if self.qualities is not None and self.qualities['NumberOfInstances'] is not None:
             fields["# of instances"] = int(self.qualities['NumberOfInstances'])
 
         # determines the order in which the information will be printed

tests/test_datasets/test_dataset.py

@@ -28,6 +28,13 @@ def setUp(self):
         self.jm1 = openml.datasets.get_dataset(1053, download_data=False)
         self.iris = openml.datasets.get_dataset(61, download_data=False)
 
+    def test_repr(self):
+        # create a bare-bones dataset as would be returned by
+        # create_dataset
+        data = openml.datasets.OpenMLDataset(name="some name",
+                                             description="a description")
+        str(data)
+
     def test_get_data_array(self):
         # Basic usage
         rval, _, categorical, attribute_names = self.dataset.get_data(dataset_format='array')