Merge lp:~cjwatson/storm/lp-psycopg-2.5 into lp:~launchpad-committers/storm/lp

[Colin Watson]

Use ABCMeta for exception base class injection

This requires Python >= 2.6 (which is unlikely to be a problem these days!),
and adds compatibility with psycopg2 >= 2.5.

Cherry-pick https://code.launchpad.net/~cjwatson/storm/psycopg-2.5/+merge/278330, proposed to mainline. This will let us upgrade Launchpad to psycopg2 >= 2.5, adding support for the json column type.

[William Grant (wgrant)]

review: Approve (code)

=== modified file 'storm/exceptions.py'
--- storm/exceptions.py	2010-10-23 21:02:22 +0000
+++ storm/exceptions.py	2015-11-23 17:31:01 +0000
@@ -18,10 +18,12 @@
 # You should have received a copy of the GNU Lesser General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
+from abc import ABCMeta
+import types
 
 
 class StormError(Exception):
-    pass
+    __metaclass__ = ABCMeta
 
 
 class CompileError(StormError):
@@ -141,5 +143,9 @@
                       OperationalError, ProgrammingError, IntegrityError,
                       DataError, NotSupportedError, InterfaceError):
         module_exception = getattr(module, exception.__name__, None)
-        if module_exception is not None:
-            module_exception.__bases__ += (exception,)
+        if (module_exception is not None and
+            isinstance(module_exception, (type, types.ClassType))):
+            # XXX This may need to be revisited when porting to Python 3 if
+            # virtual subclasses are still ignored for exception handling
+            # (https://bugs.python.org/issue12029).
+            exception.register(module_exception)