add slots to base class TransactionalContext

diff --git a/lib/sqlalchemy/engine/util.py b/lib/sqlalchemy/engine/util.py
index 7e41339bbb4c727dfced86f2cf716793ec3b6266..6aadd5c5fe169f1964d17626eebcb848d9ce6193 100644 (file)
--- a/lib/sqlalchemy/engine/util.py
+++ b/lib/sqlalchemy/engine/util.py
@@ -43,7 +43,7 @@ class TransactionalContext:
 
     """
 
-    _trans_subject = None
+    __slots__ = ("_outer_trans_ctx", "_trans_subject")
 
     def _transaction_is_active(self):
         raise NotImplementedError()