diff --git a/swh/loader/tar/loader.py b/swh/loader/tar/loader.py
index 9d2ac5d..3bff96c 100644
--- a/swh/loader/tar/loader.py
+++ b/swh/loader/tar/loader.py
@@ -1,100 +1,105 @@
 # Copyright (C) 2015-2017  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 os
 import tempfile
 import shutil
 
 from swh.loader.dir import loader
 from swh.loader.tar import tarball, utils
 from swh.model import hashutil
 
 
 class TarLoader(loader.DirLoader):
     """A tarball loader:
 
-        - creates an origin if it does not exist
-        - creates a fetch_history entry
-        - creates an origin_visit
-        - uncompress locally the tarballs in a temporary location
-        - process the content of the tarballs to persist on swh storage
-        - clean up the temporary location
-        - write an entry in fetch_history to mark the loading tarball end
-        (success or failure)
-
-        Args:
-            - tarpath: path to the tarball to uncompress
-            - origin: Dictionary origin
-              - url: url origin we fetched
-              - type: type of the origin
-            - visit_date (str): To override the visit date
-            - revision: Dictionary of information needed, keys are:
-              - author_name: revision's author name
-              - author_email: revision's author email
-              - author_date: timestamp (e.g. 1444054085)
-              - author_offset: date offset e.g. -0220, +0100
-              - committer_name: revision's committer name
-              - committer_email: revision's committer email
-              - committer_date: timestamp
-              - committer_offset: date offset e.g. -0220, +0100
-              - type: type of revision dir, tar
-              - message: synthetic message for the revision
-            - occurrences: List of occurrence dictionary.
-              Information needed, keys are:
-              - branch: occurrence's branch name
-              - authority_id: authority id (e.g. 1 for swh)
-              - validity: validity date (e.g. 2015-01-01 00:00:00+00)
+    - creates an origin if it does not exist
+    - creates a fetch_history entry
+    - creates an origin_visit
+    - uncompress locally the tarballs in a temporary location
+    - process the content of the tarballs to persist on swh storage
+    - clean up the temporary location
+    - write an entry in fetch_history to mark the loading tarball end (success
+      or failure)
+
+    Args:
+        tarpath: path to the tarball to uncompress
+        origin (dict): Dictionary with the following keys:
+
+            - url: url origin we fetched
+            - type: type of the origin
+
+        visit_date (str): To override the visit date
+        revision (dict): Dictionary of information needed, keys are:
+
+            - author_name: revision's author name
+            - author_email: revision's author email
+            - author_date: timestamp (e.g. 1444054085)
+            - author_offset: date offset e.g. -0220, +0100
+            - committer_name: revision's committer name
+            - committer_email: revision's committer email
+            - committer_date: timestamp
+            - committer_offset: date offset e.g. -0220, +0100
+            - type: type of revision dir, tar
+            - message: synthetic message for the revision
+
+        occurrences (dict): List of occurrence dictionary, with the following
+            keys:
+
+            - branch: occurrence's branch name
+            - authority_id: authority id (e.g. 1 for swh)
+            - validity: validity date (e.g. 2015-01-01 00:00:00+00)
 
     """
     CONFIG_BASE_FILENAME = 'loader/tar'
 
     ADDITIONAL_CONFIG = {
         'extraction_dir': ('string', '/tmp')
     }
 
     def __init__(self):
         super().__init__(logging_class='swh.loader.tar.TarLoader')
 
     def prepare(self, *args, **kwargs):
         """1. Uncompress the tarball in a temporary directory.
            2. Compute some metadata to update the revision.
 
         """
         tarpath, origin, visit_date, revision, occs = args
 
         if 'type' not in origin:  # let the type flow if present
             origin['type'] = 'tar'
 
         # Prepare the extraction path
         extraction_dir = self.config['extraction_dir']
         os.makedirs(extraction_dir, 0o755, exist_ok=True)
         dir_path = tempfile.mkdtemp(prefix='swh.loader.tar-',
                                     dir=extraction_dir)
 
         # add checksums in revision
         artifact = utils.convert_to_hex(hashutil.hash_path(tarpath))
         artifact['name'] = os.path.basename(tarpath)
 
         self.log.info('Uncompress %s to %s' % (tarpath, dir_path))
         nature = tarball.uncompress(tarpath, dir_path)
         artifact['archive_type'] = nature
         artifact['length'] = os.path.getsize(tarpath)
 
         revision['metadata'] = {
             'original_artifact': [artifact],
         }
 
         self.dir_path = dir_path
 
         super().prepare(dir_path, origin, visit_date, revision, None, occs)
 
     def cleanup(self):
         """Clean up temporary directory where we uncompress the tarball.
 
         """
         dir_path = self.dir_path
         if dir_path and os.path.exists(dir_path):
             shutil.rmtree(dir_path)