Introduce the hacking module to kolla

Implements: blueprint add-hacking

Change-Id: Ia24a263555b9c1eb11e61b9d3fe89612a89daed6

kolla/hacking/checks.py

+# 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.
+
+import re
+
+
+mutable_default_args = re.compile(r"^\s*def .+\((.+=\{\}|.+=\[\])")
+
+
+def no_mutable_default_args(logical_line):
+    msg = "N301: Method's default argument shouldn't be mutable!"
+    if mutable_default_args.match(logical_line):
+        yield (0, msg)
+
+
+def factory(register):
+    register(no_mutable_default_args)

tox.ini

@@ -130,3 +130,6 @@ commands=
 [flake8]
 show-source = True
 exclude=.eggs,.git,.tox,doc
+
+[hacking]
+local-check-factory = kolla.hacking.checks.factory