Merge a7477d1 into b5cf152

traits/has_traits.py

@@ -547,10 +547,10 @@ def __init__ ( self, cls, class_name, bases, class_dict, is_category ):
                     prefix_list.append( name )
                     prefix_traits[ name ] = value
 
-            elif isinstance( value, FunctionType ) or is_cython_func_or_method(value):
-                pattern = getattr( value, 'on_trait_change', None )
-                if pattern is not None:
-                    listeners[ name ] = ( 'method', pattern )
+            elif (( isinstance( value, FunctionType ) or
+                    is_cython_func_or_method(value) ) and
+                   hasattr( value, 'on_trait_change' )):
+                listeners[ name ] = ( 'method', value.on_trait_change )
 
             elif isinstance( value, property ):
                 class_traits[ name ] = generic_trait

traits/tests/test_regression.py

@@ -11,7 +11,9 @@
     from ..trait_numeric import Array
 
 from ..has_traits import HasTraits, Property, on_trait_change
-from ..trait_types import Bool, DelegatesTo, Either, Instance, Int, List
+from ..trait_types import (
+    Bool, Callable, DelegatesTo, Either, Instance, Int, List
+)
 from ..testing.unittest_tools import unittest
 
 
@@ -232,5 +234,28 @@ def test_on_trait_change_with_list_of_extended_names(self):
         self.assertTrue(model.changed)
 
 
+class TestDerivedClassDefaults(unittest.TestCase):
+
+    def test_function_default(self):
+        # Regression test for enthought/traits#411
+
+        # Given
+
+        def fun():
+            pass
+
+        class A(HasTraits):
+            f = Callable()
+
+        class B(A):
+            f = fun
+
+        # When
+        b = B()
+
+        # Then
+        self.assertIsNotNone(b.f)
+
+
 if __name__ == '__main__':
     unittest.main()