Simplify deferred creation of default values

Author: SylvainCorlay

traitlets/tests/test_traitlets.py

@@ -84,11 +84,6 @@ class A(HasTraits):
         a = A()
         self.assertEqual(a.tt, 10)
 
-        # Defaults are validated when the HasTraits is instantiated
-        class B(HasTraits):
-            tt = MyIntTT('bad default')
-        self.assertRaises(TraitError, B)
-
     def test_info(self):
         class A(HasTraits):
             tt = TraitType
@@ -118,7 +113,6 @@ def _x_default(self):
         self.assertEqual(a.x, 11)
         self.assertEqual(a._trait_values, {'x': 11})
         b = B()
-        self.assertEqual(b._trait_values, {'x': 20})
         self.assertEqual(list(a._trait_dyn_inits.keys()), ['x'])
         self.assertEqual(b.x, 20)
         c = C()
@@ -200,9 +194,9 @@ class A(HasTraits):
         a = A()
         a.on_trait_change(self.notify1)
         a.a = 0
-        self.assertEqual(len(self._notify1),0)
+        self.assertEqual(len(self._notify1), 1)
         a.b = 0.0
-        self.assertEqual(len(self._notify1),0)
+        self.assertEqual(len(self._notify1), 2)
         a.a = 10
         self.assertTrue(('a',0,10) in self._notify1)
         a.b = 10.0
@@ -213,7 +207,7 @@ class A(HasTraits):
         a.on_trait_change(self.notify1,remove=True)
         a.a = 20
         a.b = 20.0
-        self.assertEqual(len(self._notify1),0)
+        self.assertEqual(len(self._notify1), 0)
 
     def test_notify_one(self):
 
@@ -224,7 +218,7 @@ class A(HasTraits):
         a = A()
         a.on_trait_change(self.notify1, 'a')
         a.a = 0
-        self.assertEqual(len(self._notify1),0)
+        self.assertEqual(len(self._notify1), 1)
         a.a = 10
         self.assertTrue(('a',0,10) in self._notify1)
         self.assertRaises(TraitError,setattr,a,'a','bad string')
@@ -258,8 +252,8 @@ class B(A):
         b.on_trait_change(self.notify2, 'b')
         b.a = 0
         b.b = 0.0
-        self.assertEqual(len(self._notify1),0)
-        self.assertEqual(len(self._notify2),0)
+        self.assertEqual(len(self._notify1), 1)
+        self.assertEqual(len(self._notify2), 1)
         b.a = 10
         b.b = 10.0
         self.assertTrue(('a',0,10) in self._notify1)
@@ -276,7 +270,7 @@ def _a_changed(self, name, old, new):
         a = A()
         a.a = 0
         # This is broken!!!
-        self.assertEqual(len(a._notify1),0)
+        self.assertEqual(len(a._notify1), 1)
         a.a = 10
         self.assertTrue(('a',0,10) in a._notify1)
 
@@ -290,7 +284,7 @@ def _b_changed(self, name, old, new):
         b.a = 10
         b.b = 10.0
         self.assertTrue(('a',0,10) in b._notify1)
-        self.assertTrue(('b',0.0,10.0) in b._notify2)
+        self.assertTrue(('b',Undefined,10.0) in b._notify2)
 
     def test_notify_args(self):
 
@@ -500,11 +494,6 @@ class A(HasTraits):
 
         self.assertRaises(ImportError, A)
 
-        class C(HasTraits):
-            klass = Type(None, B)
-
-        self.assertRaises(TraitError, C)
-
     def test_str_klass(self):
 
         class A(HasTraits):
@@ -600,23 +589,6 @@ class C(HasTraits):
         c = C()
         self.assertTrue(c.inst is None)
 
-    def test_bad_default(self):
-        class Foo(object): pass
-
-        class A(HasTraits):
-            inst = Instance(Foo)
-
-        self.assertRaises(TraitError, A)
-
-    def test_instance(self):
-        class Foo(object): pass
-
-        def inner():
-            class A(HasTraits):
-                inst = Instance(Foo())
-
-        self.assertRaises(TraitError, inner)
-
 
 class TestThis(TestCase):
 
@@ -1368,7 +1340,7 @@ def _b_validate(self, value, trait):
         nt.assert_equal(t.a, 4)
         nt.assert_equal(changes, [])
 
-    nt.assert_equal(changes, [(0, 4)])
+    nt.assert_equal(changes, [(Undefined, 4)])
     # Test roll-back
     try:
          with t.hold_trait_notifications():

traitlets/traitlets.py

@@ -365,10 +365,9 @@ def __init__(self, default_value=NoDefaultSpecified, allow_none=None, **metadata
         else:
             self._metadata = self.metadata
 
-        self.init()
-
-    def init(self):
-        pass
+    def instance_init(self, obj):
+        self._setup_dynamic_initializer(obj)
+        super(TraitType, self).instance_init(obj)
 
     def get_default_value(self):
         """Create a new instance of the default value."""
@@ -390,22 +389,12 @@ def _setup_dynamic_initializer(self, obj):
         # trait declaration or above.
         mro = type(obj).mro()
         meth_name = '_%s_default' % self.name
-        for cls in mro[:mro.index(self.this_class)+1]:
+        for cls in mro[:mro.index(self.this_class) + 1]:
             if meth_name in cls.__dict__:
                 break
         else:
-            return False
-        # Complete the dynamic initialization.
+            return
         obj._trait_dyn_inits[self.name] = meth_name
-        return True
-
-    def _set_default_value_at_instance_init(self, obj):
-        # As above, but if no default was specified, don't try to set it.
-        # If the trait is accessed before it is given a value, init_default_value
-        # will be called at that point.
-        if (not self._setup_dynamic_initializer(obj)) \
-                and (self.default_value is not Undefined):
-            self.init_default_value(obj)
 
     def __get__(self, obj, cls=None):
         """Get the value of the trait by self.name for the instance.
@@ -569,8 +558,6 @@ def __new__(cls, *args, **kw):
             else:
                 if isinstance(value, BaseDescriptor):
                     value.instance_init(inst)
-                    if isinstance(value, TraitType) and key not in kw:
-                        value._set_default_value_at_instance_init(inst)
         inst._cross_validation_lock = False
         return inst
 
@@ -1142,7 +1129,7 @@ class Union(TraitType):
     """A trait type representing a Union type."""
 
     def __init__(self, trait_types, **metadata):
-        """Construct a Union  trait.
+        """Construct a Union trait.
 
         This trait allows values that are allowed by at least one of the
         specified trait types. A Union traitlet cannot have metadata on