Improve pep8 checking along with hacking

This change will help to check the function _() is
used but not imported. And the gates will check this missing
in the next time.

Co-authored-By: Nguyen Van Trung <trungnv@vn.fujitsu.com>

Change-Id: Icb40b3af9922e551f06cfd18de26dfcce9960d5a

ironic/drivers/modules/storage/external.py

@@ -14,6 +14,7 @@ from oslo_config import cfg
 from oslo_log import log
 
 from ironic.common import exception
+from ironic.common.i18n import _
 from ironic.drivers import base
 
 CONF = cfg.CONF

ironic/hacking/checks.py

@@ -0,0 +1,55 @@
+# Copyright 2018 FUJITSU LIMITED
+#
+# 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
+
+# D703: Found use of _() without explicit import of _!
+
+
+UNDERSCORE_IMPORT_FILES = []
+
+
+string_translation = re.compile(r"[^_]*_\(\s*('|\")")
+translated_log = re.compile(
+    r"(.)*LOG\.(audit|error|info|warn|warning|critical|exception)"
+    "\(\s*_\(\s*('|\")")
+underscore_import_check = re.compile(r"(.)*import _(.)*")
+# We need this for cases where they have created their own _ function.
+custom_underscore_check = re.compile(r"(.)*_\s*=\s*(.)*")
+
+
+def check_explicit_underscore_import(logical_line, filename):
+    """Check for explicit import of the _ function
+
+    We need to ensure that any files that are using the _() function
+    to translate logs are explicitly importing the _ function.  We
+    can't trust unit test to catch whether the import has been
+    added so we need to check for it here.
+
+    """
+
+    # Build a list of the files that have _ imported.  No further
+    # checking needed once it is found.
+    if filename in UNDERSCORE_IMPORT_FILES:
+        pass
+    elif (underscore_import_check.match(logical_line) or
+          custom_underscore_check.match(logical_line)):
+        UNDERSCORE_IMPORT_FILES.append(filename)
+    elif (translated_log.match(logical_line) or
+          string_translation.match(logical_line)):
+        yield(0, "D703: Found use of _() without explicit import of _!")
+
+
+def factory(register):
+    register(check_explicit_underscore_import)

tox.ini

@@ -135,6 +135,7 @@ max-complexity=18
 enable-extensions=H106,H203,H204,H205,H904
 
 [hacking]
+local-check-factory = ironic.hacking.checks.factory
 import_exceptions = testtools.matchers, ironic.common.i18n
 
 [testenv:lower-constraints]