diff --git a/torchreid/data/datasets/__init__.py b/torchreid/data/datasets/__init__.py
index f11d8a8..fc0d515 100644
--- a/torchreid/data/datasets/__init__.py
+++ b/torchreid/data/datasets/__init__.py
@@ -32,7 +32,8 @@ def init_image_dataset(name, **kwargs):
     """Initializes an image dataset."""
     avai_datasets = list(__image_datasets.keys())
     if name not in avai_datasets:
-        raise ValueError('Invalid dataset name. Received "{}", but expected to be one of {}'.format(name, avai_datasets))
+        raise ValueError('Invalid dataset name. Received "{}", '
+                         'but expected to be one of {}'.format(name, avai_datasets))
     return __image_datasets[name](**kwargs)
 
 
@@ -40,16 +41,17 @@ def init_video_dataset(name, **kwargs):
     """Initializes a video dataset."""
     avai_datasets = list(__video_datasets.keys())
     if name not in avai_datasets:
-        raise ValueError('Invalid dataset name. Received "{}", but expected to be one of {}'.format(name, avai_datasets))
+        raise ValueError('Invalid dataset name. Received "{}", '
+                         'but expected to be one of {}'.format(name, avai_datasets))
     return __video_datasets[name](**kwargs)
 
 
-def register_image_dataset(name, dataset_):
+def register_image_dataset(name, dataset):
     """Registers a new image dataset.
 
     Args:
         name (str): key corresponding to the new dataset.
-        dataset_ (Dataset): the new dataset class.
+        dataset (Dataset): the new dataset class.
 
     Examples::
         
@@ -67,18 +69,20 @@ def register_image_dataset(name, dataset_):
             sources=['new_dataset', 'dukemtmcreid']
         )
     """
+    global __image_datasets
     curr_datasets = list(__image_datasets.keys())
     if name in curr_datasets:
-        raise ValueError('The given name already exists, please choose another name excluding {}'.format(curr_datasets))
-    __image_datasets[name] = dataset_
+        raise ValueError('The given name already exists, please choose '
+                         'another name excluding {}'.format(curr_datasets))
+    __image_datasets[name] = dataset
 
 
-def register_video_dataset(name, dataset_):
+def register_video_dataset(name, dataset):
     """Registers a new video dataset.
 
     Args:
         name (str): key corresponding to the new dataset.
-        dataset_ (Dataset): the new dataset class.
+        dataset (Dataset): the new dataset class.
 
     Examples::
         
@@ -96,7 +100,9 @@ def register_video_dataset(name, dataset_):
             sources=['new_dataset', 'ilidsvid']
         )
     """
+    global __video_datasets
     curr_datasets = list(__video_datasets.keys())
     if name in curr_datasets:
-        raise ValueError('The given name already exists, please choose another name excluding {}'.format(curr_datasets))
-    __video_datasets[name] = dataset_
\ No newline at end of file
+        raise ValueError('The given name already exists, please choose '
+                         'another name excluding {}'.format(curr_datasets))
+    __video_datasets[name] = dataset