Merge f3ef826 into 0ec0cc7

traits/tests/test_property_notifications.py

@@ -14,7 +14,7 @@
 
 from __future__ import absolute_import
 
-from ..api import HasTraits, Property
+from ..api import HasTraits, Property, List, Int, cached_property
 
 
 class Test(HasTraits):
@@ -81,3 +81,37 @@ def test_property_notifications():
     test_7.on_trait_change(on_value_changed, 'value')
     test_7.on_trait_change(on_anyvalue_changed)
     test_7.value = 'test 7'
+
+
+class Entity(HasTraits):
+    val = Int
+
+class WrongEntity(HasTraits):
+    val2 = Int
+
+class WithList(HasTraits):
+    mylist = List
+    prop = Property(depends_on='mylist[], mylist.val')
+
+    @cached_property
+    def _get_prop(self):
+        return sum(i.val for i in self.mylist if isinstance(i, Entity))
+
+def test_property_notification_with_lists():
+    v1 = Entity(val=1)
+    v2 = Entity(val=2)
+    sl = WithList()
+    assert sl.prop == 0
+
+    sl.mylist = [v1, v2]
+    assert sl.prop == 3
+
+    v3 = WrongEntity(val2=3)  #Entity without proper attribute should not trigger property notification
+    sl.mylist.append(v3)
+    assert sl.prop == 3
+
+    sl.mylist = [v1,v2, v3, 2] #please do not mind if non-HasTraits object is in list
+    assert sl.prop == 3
+
+    sl.mylist.append(v1)
+    assert sl.prop == 4

traits/traits_listener.py

@@ -32,7 +32,7 @@
 from string import whitespace
 from types import MethodType
 
-from .has_traits import HasPrivateTraits
+from .has_traits import HasPrivateTraits, HasTraits
 from .trait_base import Undefined, Uninitialized
 from .traits import Property
 from .trait_types import Str, Int, Bool, Instance, List, Enum, Any
@@ -341,7 +341,7 @@ def register ( self, new ):
         """
         # Make sure we actually have an object to set listeners on and that it
         # has not already been registered (cycle breaking):
-        if (new is None) or (new is Undefined) or (new in self.active):
+        if not isinstance(new, HasTraits) or new in self.active:
             return INVALID_DESTINATION
 
         # Create a dictionary of {name: trait_values} that match the object's