[Zope3-checkins] CVS: Zope3/lib/python/Persistence - patch.py:1.6

[Jeremy Hylton]

Update of /cvs-repository/Zope3/lib/python/Persistence
In directory cvs.zope.org:/tmp/cvs-serv23954/Persistence

Modified Files:
	patch.py 
Log Message:
Preserve MRO linearizability when add Persistent to bases.


=== Zope3/lib/python/Persistence/patch.py 1.5 => 1.6 ===
--- Zope3/lib/python/Persistence/patch.py:1.5	Fri Nov 22 11:54:38 2002
+++ Zope3/lib/python/Persistence/patch.py	Fri Nov 22 15:08:21 2002
@@ -124,11 +124,24 @@
 class TypeWrapper(Wrapper):
 
     def unwrap(self, bases, dict):
-        # Must add Persistent to the list of bases so that type (the
+        # XXX Add Persistent to the list of bases so that type (the
         # base class of PersistentClassMetaClass) will create the
         # correct C layout.
-        return PersistentClassMetaClass(self._obj.__name__,
-                                        bases + (Persistent,), dict)
+        
+        # We must maintain a linearizable MRO when adding Persistent
+        # to list of bases.  In particular, object is in Persistent's
+        # __bases__ to Persistent must occur before object in the
+        # new class's __bases__.
+
+        if not Persistent in bases:
+            if object in bases:
+                L = list(bases)
+                i = L.index(object)
+                newbases = bases[:i] + (Persistent,) + bases[i:]
+            else:
+                newbases = bases + (Persistent,)
+        
+        return PersistentClassMetaClass(self._obj.__name__, newbases, dict)
 
 class Pickler(pickle.Pickler):