Merge pull request #5502 from Zaharid/iniinstance

Containers resolve instances (traits).

IPython/utils/tests/test_traitlets.py

@@ -898,6 +898,25 b' class TestList(TraitTestBase):'
             value = list(value)
         return value
 
+class Foo(object):
+    pass
+
+class InstanceListTrait(HasTraits):
+
+    value = List(Instance(__name__+'.Foo'))
+
+class TestInstanceList(TraitTestBase):
+
+    obj = InstanceListTrait()
+
+    def test_klass(self):
+        """Test that the instance klass is properly assigned."""
+        self.assertIs(self.obj.traits()['value']._trait.klass, Foo)
+
+    _default_value = []
+    _good_values = [[Foo(), Foo(), None], None]
+    _bad_values = [['1', 2,], '1', [Foo]]
+
 class LenListTrait(HasTraits):
 
     value = List(Int, [0], minlen=1, maxlen=2)

IPython/utils/traitlets.py

@@ -1284,6 +1284,11 b' class Container(Instance):'
                 validated.append(v)
         return self.klass(validated)
 
+    def instance_init(self, obj):
+        if isinstance(self._trait, Instance):
+            self._trait._resolve_classes()
+        super(Container, self).instance_init(obj)
+
 
 class List(Container):
     """An instance of a Python list."""