BUG: Do not store class-specific state on TraitTypes since they may be shared through subclassing.

IPython/utils/tests/test_traitlets.py

@@ -142,15 +142,27 b' class TestTraitType(TestCase):'
 
         a = A()
         self.assertEquals(a._trait_values, {})
+        self.assertEquals(a._trait_dyn_inits.keys(), ['x'])
         self.assertEquals(a.x, 11)
         self.assertEquals(a._trait_values, {'x': 11})
         b = B()
         self.assertEquals(b._trait_values, {'x': 20})
+        self.assertEquals(a._trait_dyn_inits.keys(), ['x'])
         self.assertEquals(b.x, 20)
         c = C()
         self.assertEquals(c._trait_values, {})
+        self.assertEquals(a._trait_dyn_inits.keys(), ['x'])
         self.assertEquals(c.x, 21)
         self.assertEquals(c._trait_values, {'x': 21})
+        # Ensure that the base class remains unmolested when the _default
+        # initializer gets overridden in a subclass.
+        a = A()
+        c = C()
+        self.assertEquals(a._trait_values, {})
+        self.assertEquals(a._trait_dyn_inits.keys(), ['x'])
+        self.assertEquals(a.x, 11)
+        self.assertEquals(a._trait_values, {'x': 11})
+
 
 
 class TestHasTraitsMeta(TestCase):

IPython/utils/traitlets.py

@@ -262,7 +262,7 b' class TraitType(object):'
             obj._trait_values[self.name] = newdv
             return
         # Complete the dynamic initialization.
-        self.dynamic_initializer = cls.__dict__[meth_name]
+        obj._trait_dyn_inits[self.name] = cls.__dict__[meth_name]
 
     def __get__(self, obj, cls=None):
         """Get the value of the trait by self.name for the instance.
@@ -279,8 +279,8 b' class TraitType(object):'
                 value = obj._trait_values[self.name]
             except KeyError:
                 # Check for a dynamic initializer.
-                if hasattr(self, 'dynamic_initializer'):
-                    value = self.dynamic_initializer(obj)
+                if self.name in obj._trait_dyn_inits:
+                    value = obj._trait_dyn_inits[self.name](obj)
                     # FIXME: Do we really validate here?
                     value = self._validate(obj, value)
                     obj._trait_values[self.name] = value
@@ -318,11 +318,6 b' class TraitType(object):'
         else:
             return value
 
-    def set_dynamic_initializer(self, method):
-        """ Set the dynamic initializer method, if any.
-        """
-        self.dynamic_initializer = method
-
     def info(self):
         return self.info_text
 
@@ -399,6 +394,7 b' class HasTraits(object):'
             inst = new_meth(cls, **kw)
         inst._trait_values = {}
         inst._trait_notifiers = {}
+        inst._trait_dyn_inits = {}
         # Here we tell all the TraitType instances to set their default
         # values on the instance. 
         for key in dir(cls):