Merge pull request #8273 from SylvainCorlay/fixes_widget_serialization

Minor fixes on custom serialization, and traitlet hold_traits

IPython/core/application.py

@@ -215,7 +215,7 b' class BaseIPythonApplication(Application):'
             return crashhandler.crash_handler_lite(etype, evalue, tb)
     
     def _ipython_dir_changed(self, name, old, new):
-        if old is not None and old is not Undefined:
+        if old is not Undefined:
             str_old = py3compat.cast_bytes_py2(os.path.abspath(old),
                 sys.getfilesystemencoding()
             )

IPython/html/static/widgets/js/widget.js

@@ -369,7 +369,7 b' define(["widgets/js/manager",'
             // being the value or the promise of the serialized value
             var serializers = this.constructor.serializers;
             if (serializers) {
-                for (k in attrs) {
+                for (var k in attrs) {
                     if (serializers[k] && serializers[k].serialize) {
                         attrs[k] = (serializers[k].serialize)(attrs[k], this);
                     }
@@ -383,6 +383,7 b' define(["widgets/js/manager",'
                 for (var i=0; i<keys.length; i++) {
                     var key = keys[i];
                     var value = state[key];
+                    if (value) {
                     if (value.buffer instanceof ArrayBuffer
                         || value instanceof ArrayBuffer) {
                         buffers.push(value);
@@ -390,6 +391,7 b' define(["widgets/js/manager",'
                         delete state[key];
                     }
                 }
+                }
                 that.comm.send({method: 'backbone', sync_data: state, buffer_keys: buffer_keys}, callbacks, {}, buffers);
             }).catch(function(error) {
                 that.pending_msgs--;

traitlets/tests/test_traitlets.py

@@ -1376,6 +1376,24 b' def test_hold_trait_notifications():'
     nt.assert_equal(t.b, 0)
     
 
+class RollBack(HasTraits):
+    bar = Int()
+    def _bar_validate(self, value, trait):
+        if value:
+            raise TraitError('foobar')
+        return value
+
+
+class TestRollback(TestCase):
+
+    def test_roll_back(self):
+
+        def assign_rollback():
+            RollBack(bar=1)
+
+        self.assertRaises(TraitError, assign_rollback)
+
+
 class OrderTraits(HasTraits):
     notified = Dict()
     

traitlets/traitlets.py

@@ -623,7 +623,7 b' class HasTraits(py3compat.with_metaclass(MetaHasTraits, object)):'
                     if cache[name][1] is not Undefined:
                         setattr(self, name, cache[name][1])
                     else:
-                        delattr(self, name)
+                        self._trait_values.pop(name)
                 cache = {}
                 raise e
             finally: