Merge pull request #7762 from SylvainCorlay/fix_parameterized_trait

No default value creation for element traits of a List

IPython/utils/tests/test_traitlets.py

@@ -972,6 +972,19 b' class TestList(TraitTestBase):'
 class Foo(object):
     pass
 
+class NoneInstanceListTrait(HasTraits):
+    
+    value = List(Instance(Foo, allow_none=False))
+
+class TestNoneInstanceList(TraitTestBase):
+
+    obj = NoneInstanceListTrait()
+
+    _default_value = []
+    _good_values = [[Foo(), Foo()], []]
+    _bad_values = [[None], [Foo(), None]]
+
+
 class InstanceListTrait(HasTraits):
 
     value = List(Instance(__name__+'.Foo'))

IPython/utils/traitlets.py

@@ -1461,8 +1461,8 b' class Container(Instance):'
     def instance_init(self, obj):
         if isinstance(self._trait, TraitType):
             self._trait.this_class = self.this_class
-        if hasattr(self._trait, 'instance_init'):
-            self._trait.instance_init(obj)
+        if hasattr(self._trait, '_resolve_classes'):
+            self._trait._resolve_classes()
         super(Container, self).instance_init(obj)
 
 
@@ -1631,6 +1631,14 b' class Tuple(Container):'
                 validated.append(v)
         return tuple(validated)
 
+    def instance_init(self, obj):
+        for trait in self._traits:
+            if isinstance(trait, TraitType):
+                trait.this_class = self.this_class
+            if hasattr(trait, '_resolve_classes'):
+                trait._resolve_classes()
+        super(Container, self).instance_init(obj)
+
 
 class Dict(Instance):
     """An instance of a Python dict."""