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.

Change-Id: Ic1dd25e99c3db9fc8782a5f0977679978e274191

kolla/hacking/checks.py

@@ -15,6 +15,40 @@ import re
 
 mutable_default_args = re.compile(r"^\s*def .+\((.+=\{\}|.+=\[\])")
 
+# 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 no_log_warn(logical_line):
     """Disallow 'LOG.warn('
@@ -36,5 +70,6 @@ def no_mutable_default_args(logical_line):
 
 
 def factory(register):
+    register(check_explicit_underscore_import)
     register(no_mutable_default_args)
     register(no_log_warn)