diff --git a/doc/ext/support_matrix.py b/doc/ext/support_matrix.py
index f99ff78cd5d3..96e0b379e97c 100644
--- a/doc/ext/support_matrix.py
+++ b/doc/ext/support_matrix.py
@@ -25,7 +25,6 @@ It is used via a single directive in the .rst file
 import re
 import sys
 
-import six
 from six.moves import configparser
 
 from docutils import nodes
@@ -59,7 +58,9 @@ class SupportMatrixFeature(object):
                   STATUS_CONDITION, STATUS_OPTIONAL]
 
     def __init__(self, key, title, status=STATUS_OPTIONAL,
-                 group=None, notes=None, cli=[]):
+                 group=None, notes=None, cli=None):
+        if not cli:
+            cli = []
         # A unique key (eg 'foo.bar.wizz') to identify the feature
         self.key = key
         # A human friendly short title for the feature
@@ -474,10 +475,10 @@ class SupportMatrixDirective(rst.Directive):
             notes.append(item)
 
     def _create_cli_paragraph(self, feature):
-        ''' Create a paragraph which represents the CLI commands of the feature
+        """Create a paragraph which represents the CLI commands of the feature
 
         The paragraph will have a bullet list of CLI commands.
-        '''
+        """
         para = nodes.paragraph()
         para.append(nodes.strong(text="CLI commands:"))
         commands = nodes.bullet_list()
@@ -489,7 +490,7 @@ class SupportMatrixDirective(rst.Directive):
         return para
 
     def _create_notes_paragraph(self, notes):
-        """ Constructs a paragraph which represents the implementation notes
+        """Constructs a paragraph which represents the implementation notes
 
         The paragraph consists of text and clickable URL nodes if links were
         given in the notes.
diff --git a/doc/ext/versioned_notifications.py b/doc/ext/versioned_notifications.py
index da0b2f82bf6f..64b3babba91d 100644
--- a/doc/ext/versioned_notifications.py
+++ b/doc/ext/versioned_notifications.py
@@ -22,8 +22,8 @@ It is used via a single directive in the .rst file
 
 from docutils import nodes
 import importlib
-from sphinx.util.compat import Directive
 import pkgutil
+from sphinx.util.compat import Directive
 
 import nova.notifications.objects
 from nova.notifications.objects import base as notification
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 3e36ed925458..ee058977b69c 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -1,12 +1,24 @@
-# nova documentation build configuration file
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+#  nova documentation build configuration file
 #
 # Refer to the Sphinx documentation for advice on configuring this file:
 #
 #   http://www.sphinx-doc.org/en/stable/config.html
 
+import os
 import subprocess
 import sys
-import os
 import warnings
 
 from nova.version import version_info
diff --git a/tox.ini b/tox.ini
index ab8e371246ce..937b93db65c5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -177,7 +177,7 @@ commands = bash -c tools/releasenotes_tox.sh
 
 enable-extensions = H106,H203,H904
 ignore = E121,E122,E123,E124,E125,E126,E127,E128,E129,E131,E251,H405
-exclude =  .venv,.git,.tox,dist,doc,*lib/python*,*egg,build,tools/xenserver*,releasenotes
+exclude =  .venv,.git,.tox,dist,*lib/python*,*egg,build,tools/xenserver*,releasenotes
 # To get a list of functions that are more complex than 25, set max-complexity
 # to 25 and run 'tox -epep8'.
 # 34 is currently the most complex thing we have