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

[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.

Use ABCMeta for exception base class injection.

This lets us be compatible with psycopg2 >= 2.5, where Error and subclasses are implemented in a C extension so can't have their __bases__ attribute patched.

It does introduce a potential obstacle to porting to Python 3 due to a Python bug noted in a comment. Other possible approaches include converting StormError et al into tuples (but that would be an API break if anyone was using them for any purpose other than isinstance/issubclass/exception-handling) or re-raising all database exceptions as Storm exceptions (rather intrusive and possibly error-prone). Since Storm hasn't yet been ported to Python 3 anyway, this doesn't seem like a showstopper, and I think using ABCMeta is a pragmatic approach for the time being.

[Adam Collard (adam-collard)]

Looks good to me! +1

review: Approve

[Björn Tillenius (bjornt)]

Looks good to me as well, +1!

I've confirmed both Landscape and Storm tests pass with this branch and python-psycopg2 2.6.1-1build1.

There are some django tests that fail in Storm, but they fail in trunk as well for me.

review: Approve

=== modified file 'storm/exceptions.py'
--- storm/exceptions.py	2010-10-23 21:02:22 +0000
+++ storm/exceptions.py	2015-11-23 15:14:11 +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)