merge 0.6 series to trunk.

1 files changed, 1 insertions, 4 deletions

diff --git a/lib/sqlalchemy/sql/visitors.py b/lib/sqlalchemy/sql/visitors.py
index a5bd497ae..4471d4fb0 100644
--- a/lib/sqlalchemy/sql/visitors.py
+++ b/lib/sqlalchemy/sql/visitors.py
@@ -34,13 +34,10 @@ class VisitableType(type):
     """
     
     def __init__(cls, clsname, bases, clsdict):
-        if cls.__name__ == 'Visitable':
+        if cls.__name__ == 'Visitable' or not hasattr(cls, '__visit_name__'):
             super(VisitableType, cls).__init__(clsname, bases, clsdict)
             return
         
-        assert hasattr(cls, '__visit_name__'), "`Visitable` descendants " \
-                                               "should define `__visit_name__`"
-        
         # set up an optimized visit dispatch function
         # for use by the compiler
         visit_name = cls.__visit_name__