diff --git a/swh/objstorage/cloud/objstorage_cloud.py b/swh/objstorage/cloud/objstorage_cloud.py
index ef78b18..1c2ca5e 100644
--- a/swh/objstorage/cloud/objstorage_cloud.py
+++ b/swh/objstorage/cloud/objstorage_cloud.py
@@ -1,169 +1,169 @@
 # Copyright (C) 2016-2017  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import abc
 
 from swh.model import hashutil
 from swh.objstorage.objstorage import ObjStorage, compute_hash
 from swh.objstorage.exc import ObjNotFoundError, Error
 
 from libcloud.storage import providers
 from libcloud.storage.types import Provider, ObjectDoesNotExistError
 
 
 class CloudObjStorage(ObjStorage, metaclass=abc.ABCMeta):
     """Abstract ObjStorage that connect to a cloud using Libcloud
 
     Implementations of this class must redefine the _get_provider
     method to make it return a driver provider (i.e. object that
     supports `get_driver` method) which return a LibCloud driver (see
     https://libcloud.readthedocs.io/en/latest/storage/api.html).
 
     """
     def __init__(self, api_key, api_secret_key, container_name, **kwargs):
         super().__init__(**kwargs)
         self.driver = self._get_driver(api_key, api_secret_key)
         self.container_name = container_name
         self.container = self.driver.get_container(
             container_name=container_name)
 
     def _get_driver(self, api_key, api_secret_key):
         """Initialize a driver to communicate with the cloud
 
         Args:
             api_key: key to connect to the API.
             api_secret_key: secret key for authentication.
 
         Returns:
             a Libcloud driver to a cloud storage.
 
         """
         # Get the driver class from its description.
         cls = providers.get_driver(self._get_provider())
         # Initialize the driver.
         return cls(api_key, api_secret_key)
 
     @abc.abstractmethod
     def _get_provider(self):
         """Get a libcloud driver provider
 
         This method must be overridden by subclasses to specify which
         of the native libcloud driver the current storage should
         connect to.  Alternatively, provider for a custom driver may
         be returned, in which case the provider will have to support
         `get_driver` method.
 
         """
         raise NotImplementedError('%s must implement `get_provider` method'
                                   % type(self))
 
     def check_config(self, *, check_write):
         """Check the configuration for this object storage"""
         # FIXME: hopefully this blew up during instantiation
         return True
 
     def __contains__(self, obj_id):
         try:
             self._get_object(obj_id)
         except ObjNotFoundError:
             return False
         else:
             return True
 
     def __iter__(self):
         """ Iterate over the objects present in the storage
 
         Warning: Iteration over the contents of a cloud-based object storage
         may have bad efficiency: due to the very high amount of objects in it
         and the fact that it is remote, get all the contents of the current
         object storage may result in a lot of network requests.
 
         You almost certainly don't want to use this method in production.
         """
         yield from map(lambda obj: obj.name,
                        self.driver.iterate_container_objects(self.container))
 
     def __len__(self):
         """Compute the number of objects in the current object storage.
 
         Warning: this currently uses `__iter__`, its warning about bad
         performance applies.
 
         Returns:
             number of objects contained in the storage.
 
         """
         return sum(1 for i in self)
 
     def add(self, content, obj_id=None, check_presence=True):
         if obj_id is None:
             # Checksum is missing, compute it on the fly.
             obj_id = compute_hash(content)
 
         if check_presence and obj_id in self:
             return obj_id
 
         self._put_object(content, obj_id)
         return obj_id
 
     def restore(self, content, obj_id=None):
         return self.add(content, obj_id, check_presence=False)
 
     def get(self, obj_id):
         return bytes(self._get_object(obj_id).as_stream())
 
     def check(self, obj_id):
         # Check that the file exists, as _get_object raises ObjNotFoundError
         self._get_object(obj_id)
         # Check the content integrity
         obj_content = self.get(obj_id)
         content_obj_id = compute_hash(obj_content)
         if content_obj_id != obj_id:
             raise Error(obj_id)
 
     def delete(self, obj_id):
         super().delete(obj_id)  # Check delete permission
         obj = self._get_object(obj_id)
         return self.driver.delete_object(obj)
 
     def _get_object(self, obj_id):
         """Get a Libcloud wrapper for an object pointer.
 
         This wrapper does not retrieve the content of the object
         directly.
 
         """
         hex_obj_id = hashutil.hash_to_hex(obj_id)
         try:
             return self.driver.get_object(self.container_name, hex_obj_id)
-        except ObjectDoesNotExistError as e:
+        except ObjectDoesNotExistError:
             raise ObjNotFoundError(obj_id)
 
     def _put_object(self, content, obj_id):
         """Create an object in the cloud storage.
 
         Created object will contain the content and be referenced by
         the given id.
 
         """
         hex_obj_id = hashutil.hash_to_hex(obj_id)
         self.driver.upload_object_via_stream(iter(content), self.container,
                                              hex_obj_id)
 
 
 class AwsCloudObjStorage(CloudObjStorage):
     """ Amazon's S3 Cloud-based object storage
 
     """
     def _get_provider(self):
         return Provider.S3
 
 
 class OpenStackCloudObjStorage(CloudObjStorage):
     """ OpenStack Swift Cloud based object storage
 
     """
     def _get_provider(self):
         return Provider.OPENSTACK_SWIFT