Add H203: Check for Python 3.x compatible except

Python 3.x deprecated 'except x,y:'
Enforce 'except x as y:' instead.

Change-Id: I0bd89fa05d88de34ca62ce59f427468ede226126

HACKING.rst

@@ -210,6 +210,25 @@ Example::
     LOG.error(msg % {"s_id": "1234", "m_key": "imageId"})
 
 
+Python 3.x compatibility
+------------------------
+OpenStack code should become Python 3.x compatible. That means all Python 2.x-only
+constructs or dependencies should be avoided. An example is
+
+    except x,y:
+
+Use
+
+    except x as y:
+
+instead. Other Python 3.x compatility issues, like e.g. print operator
+can be avoided in new code by using
+
+    from __future__ import print_function
+
+at the top of your module.
+
+
 Creating Unit Tests
 -------------------
 For every new feature, unit tests should be created that both test and

hacking/core.py

@@ -214,6 +214,29 @@ def hacking_except_format_assert(logical_line):
         yield 1, "H202: assertRaises Exception too broad"
 
 
+@flake8ext
+def hacking_except_python3x_compatible(logical_line):
+    r"""Check for except statements to be Python 3.x compatible
+
+    As of Python 3.x, the construct 'except x,y:' has been removed.
+    Use 'except x as y:' instead.
+
+
+    Okay: try:\n    pass\nexcept Exception:\n    pass
+    Okay: try:\n    pass\nexcept (Exception, AttributeError):\n    pass
+    H203: try:\n    pass\nexcept AttributeError, e:\n    pass
+    """
+
+    def is_old_style_except(logical_line):
+        return (',' in logical_line
+                and ')' not in logical_line.rpartition(',')[2])
+
+    if (logical_line.startswith("except ")
+            and logical_line.endswith(':')
+            and is_old_style_except(logical_line)):
+        yield 0, "H203: Python 3.x incompatible 'except x,y:' construct"
+
+
 modules_cache = dict((mod, True) for mod in tuple(sys.modules.keys())
                      + sys.builtin_module_names)
 
@@ -266,7 +289,7 @@ def hacking_import_rules(logical_line, filename):
             try:
                 # NOTE(vish): handle namespace modules
                 __import__(mod)
-            except ImportError, exc:
+            except ImportError as exc:
                 # NOTE(vish): the import error might be due
                 #             to a missing dependency
                 missing = str(exc).split()[-1]

setup.cfg

@@ -31,6 +31,7 @@ flake8.extension =
     H102 = hacking.core:hacking_has_license
     H201 = hacking.core:hacking_except_format
     H202 = hacking.core:hacking_except_format_assert
+    H203 = hacking.core:hacking_except_python3x_compatible
     H301 = hacking.core:hacking_import_rules
     H306 = hacking.core:hacking_import_alphabetical
     H401 = hacking.core:hacking_docstring_start_space