Merge pull request #266 from burnpanck/fix-trait-error-handler-py3

Trait exception handlers should be able to access the exception

traits/tests/test_listeners.py

@@ -75,6 +75,11 @@ def alt_weight_changed(self, object, name, old, new):
         events["alt_weight_changed"] = (name, old, new)
 
 
+class GenerateFailingEvents(HasTraits):
+    name = Str
+    def _name_changed(self):
+        raise RuntimeError
+
 class Test_Listeners(unittest.TestCase):
 
     def test(self):
@@ -124,6 +129,24 @@ def test(self):
         ge.trait_set(name='Ralph', age=29, weight=198.0)
         self.assertEqual(events, {})
 
+    def test_trait_exception_handler_can_access_exception(self):
+        """ Tests if trait exception handlers can access the traceback of the exception.
+        """
+        import traceback
+
+        from traits import trait_notifiers
+        def _handle_exception(obj,name,old,new):
+            self.assertIsNotNone(sys.exc_info()[0])
+        ge = GenerateFailingEvents()
+        try:
+            trait_notifiers.push_exception_handler(
+                _handle_exception,
+                reraise_exceptions=False,
+                main=True
+            )
+            ge.trait_set(name='John Cleese')
+        finally:
+            trait_notifiers.pop_exception_handler()
 
 class A(HasTraits):
     exception = Any

traits/trait_notifiers.py

@@ -339,17 +339,16 @@ def __call__ ( self, object, trait_name, old, new ):
                 # Call the handler.
                 self.handler( *args )
             except Exception as e:
-                exception = e
-            else:
-                exception = None
-            finally:
                 if _post_change_event_tracer is not None:
                     _post_change_event_tracer( object, trait_name, old, new,
                                                self.handler,
-                                               exception=exception )
-
-            if exception is not None:
+                                               exception=e )
                 handle_exception( object, trait_name, old, new )
+            else:
+                if _post_change_event_tracer is not None:
+                    _post_change_event_tracer( object, trait_name, old, new,
+                                               self.handler,
+                                               exception=None )
 
     def equals ( self, handler ):
         return False