- add an example illustrating attribute event reception.

2 files changed, 12 insertions, 6 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index 2d7c726a1..e67026eea 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -1545,7 +1545,10 @@ class InstrumentationRegistry(object):
     def state_of(self, instance):
         if instance is None:
             raise AttributeError("None has no persistent state.")
-        return self.state_finders[instance.__class__](instance)
+        try:
+            return self.state_finders[instance.__class__](instance)
+        except KeyError:
+            raise AttributeError("%r is not instrumented" % instance.__class__)
 
     def state_or_default(self, instance, default=None):
         if instance is None:
diff --git a/lib/sqlalchemy/orm/interfaces.py b/lib/sqlalchemy/orm/interfaces.py
index ff15062aa..6dd2225c8 100644
--- a/lib/sqlalchemy/orm/interfaces.py
+++ b/lib/sqlalchemy/orm/interfaces.py
@@ -702,17 +702,20 @@ class PropertyOption(MapperOption):
         return l
 
 class AttributeExtension(object):
-    """An abstract class which specifies `append`, `delete`, and `set`
-    event handlers to be attached to an object property.
+    """An event handler for individual attribute change events.
+    
+    AttributeExtension is assembled within the descriptors associated 
+    with a mapped class.
+    
     """
 
-    def append(self, obj, child, initiator):
+    def append(self, state, value, initiator):
         pass
 
-    def remove(self, obj, child, initiator):
+    def remove(self, state, value, initiator):
         pass
 
-    def set(self, obj, child, oldchild, initiator):
+    def set(self, state, value, oldvalue, initiator):
         pass