HACKING fixes, sqlalchemy fix.

Add exceptions to hacking.py make sqlalchemy stuff legal and prevent
clutter.

Change-Id: I44b100b4c0c4dfcec81beea7aba2d8598d5a08d0

2 files changed, 21 insertions, 6 deletions

diff --git a/HACKING.rst b/HACKING.rst
index e1fc99fd9..467248e0e 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -28,12 +28,18 @@ General
 
 Imports
 -------
-- Do not import objects, only modules
-- Do not import more than one module per line
+- Do not import objects, only modules (*)
+- Do not import more than one module per line (*)
 - Do not make relative imports
 - Order your imports by the full module path
 - Organize your imports according to the following template
 
+(*) exceptions are:
+
+- imports from ``migrate`` package
+- imports from ``sqlalchemy`` package
+- imports from ``nova.db.sqlalchemy.session`` module
+
 Example::
 
   # vim: tabstop=4 shiftwidth=4 softtabstop=4
diff --git a/tools/hacking.py b/tools/hacking.py
index 7aa756bb5..c3c1d7156 100755
--- a/tools/hacking.py
+++ b/tools/hacking.py
@@ -36,6 +36,13 @@ import pep8
 #N5xx dictionaries/lists
 #N6xx Calling methods
 
+IMPORT_EXCEPTIONS = ['sqlalchemy', 'migrate', 'nova.db.sqlalchemy.session']
+
+
+def is_import_exception(mod):
+    return mod in IMPORT_EXCEPTIONS or \
+        any(mod.startswith(m + '.') for m in IMPORT_EXCEPTIONS)
+
 
 def nova_todo_format(physical_line):
     """
@@ -77,13 +84,13 @@ def nova_one_import_per_line(logical_line):
 
     Examples:
     BAD: from nova.rpc.common import RemoteError, LOG
-    BAD: from sqlalchemy import MetaData, Table
     N301
     """
     pos = logical_line.find(',')
-    if (pos > -1 and (logical_line.startswith("import ") or
-       (logical_line.startswith("from ") and
-       logical_line.split()[2] == "import"))):
+    parts = logical_line.split()
+    if pos > -1 and (parts[0] == "import" or
+       parts[0] == "from" and parts[2] == "import") and \
+       not is_import_exception(parts[1]):
         return pos, "NOVA N301: one import per line"
 
 
@@ -104,6 +111,8 @@ def nova_import_module_only(logical_line):
         try:
             valid = True
             if parent:
+                if is_import_exception(parent):
+                    return
                 parent_mod = __import__(parent, globals(), locals(), [mod], -1)
                 valid = inspect.ismodule(getattr(parent_mod, mod))
             else: