- simplified _mapper_registry further. its now just a weakkeydict of mapper->True, stores

all mappers including non primaries, and is strictly used for the list of "to compile/dispose".
- all global references are now weak referencing.  if you del a mapped class and any dependent classes,
its mapper and all dependencies fall out of scope.
- attributes.py still had issues which were barely covered by tests.  added way more tests (coverage.py still says 71%, doh)
fixed things, took out unnecessary commit to states.  attribute history is also asserted for ordering.

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/sqlalchemy/util.py b/lib/sqlalchemy/util.py
index 3e26217c9..463d4b8af 100644
--- a/lib/sqlalchemy/util.py
+++ b/lib/sqlalchemy/util.py
@@ -4,7 +4,7 @@
 # This module is part of SQLAlchemy and is released under
 # the MIT License: http://www.opensource.org/licenses/mit-license.php
 
-import itertools, sys, warnings, sets
+import itertools, sys, warnings, sets, weakref
 import __builtin__
 
 from sqlalchemy import exceptions, logging
@@ -113,7 +113,7 @@ def flatten_iterator(x):
             yield elem
 
 class ArgSingleton(type):
-    instances = {}
+    instances = weakref.WeakValueDictionary()
 
     def dispose(cls):
         for key in list(ArgSingleton.instances):