Merge pull request #8124 from jdfreder/dynamic

Dynamic traits.

IPython/html/widgets/widget.py

@@ -292,6 +292,13 b' class Widget(LoggingConfigurable):'
             True if the callback should be unregistered."""
         self._display_callbacks.register_callback(callback, remove=remove)
 
+    def add_trait(self, traitname, trait):
+        """Dynamically add a trait attribute to the Widget."""
+        super(Widget, self).add_trait(traitname, trait)
+        if trait.get_metadata('sync'):
+             self.keys.append(traitname)
+             self.send_state(traitname)
+
     #-------------------------------------------------------------------------
     # Support methods
     #-------------------------------------------------------------------------

IPython/utils/tests/test_traitlets.py

@@ -1563,3 +1563,55 b' class TestForwardDeclaredTypeList(TraitTestBase):'
 ###
 # End Forward Declaration Tests
 ###
+
+class TestDynamicTraits(TestCase):
+
+    def setUp(self):
+        self._notify1 = []
+
+    def notify1(self, name, old, new):
+        self._notify1.append((name, old, new))
+
+    def test_notify_all(self):
+
+        class A(HasTraits):
+            pass
+
+        a = A()
+        self.assertTrue(not hasattr(a, 'x'))
+        self.assertTrue(not hasattr(a, 'y'))
+
+        # Dynamically add trait x.
+        a.add_trait('x', Int())
+        self.assertTrue(hasattr(a, 'x'))
+        self.assertTrue(isinstance(a, (A, )))
+
+        # Dynamically add trait y.
+        a.add_trait('y', Float())
+        self.assertTrue(hasattr(a, 'y'))
+        self.assertTrue(isinstance(a, (A, )))
+        self.assertEqual(a.__class__.__name__, A.__name__)
+
+        # Create a new instance and verify that x and y
+        # aren't defined.
+        b = A()
+        self.assertTrue(not hasattr(b, 'x'))
+        self.assertTrue(not hasattr(b, 'y'))
+
+        # Verify that notification works like normal.
+        a.on_trait_change(self.notify1)
+        a.x = 0
+        self.assertEqual(len(self._notify1), 0)
+        a.y = 0.0
+        self.assertEqual(len(self._notify1), 0)
+        a.x = 10
+        self.assertTrue(('x', 0, 10) in self._notify1)
+        a.y = 10.0
+        self.assertTrue(('y', 0.0, 10.0) in self._notify1)
+        self.assertRaises(TraitError, setattr, a, 'x', 'bad string')
+        self.assertRaises(TraitError, setattr, a, 'y', 'bad string')
+        self._notify1 = []
+        a.on_trait_change(self.notify1, remove=True)
+        a.x = 20
+        a.y = 20.0
+        self.assertEqual(len(self._notify1), 0)

IPython/utils/traitlets.py

@@ -804,6 +804,12 b' class HasTraits(py3compat.with_metaclass(MetaHasTraits, object)):'
         else:
             return trait.get_metadata(key, default)
 
+    def add_trait(self, traitname, trait):
+        """Dynamically add a trait attribute to the HasTraits instance."""
+        self.__class__ = type(self.__class__.__name__, (self.__class__,),
+                              {traitname: trait})
+        trait.set_default_value(self)
+
 #-----------------------------------------------------------------------------
 # Actual TraitTypes implementations/subclasses
 #-----------------------------------------------------------------------------