Merge pull request #38 from SylvainCorlay/has_trait

has_trait function

docs/source/using_traitlets.rst

@@ -7,6 +7,8 @@ Any class with traitlet attributes must inherit from :class:`HasTraits`.
 
 .. autoclass:: HasTraits
 
+   .. automethod:: has_trait
+
    .. automethod:: trait_names
 
    .. automethod:: class_trait_names

traitlets/tests/test_traitlets.py

@@ -374,6 +374,8 @@ class A(HasTraits):
         a = A()
         self.assertEqual(sorted(a.trait_names()),['f','i'])
         self.assertEqual(sorted(A.class_trait_names()),['f','i'])
+        self.assertTrue(a.has_trait('f'))
+        self.assertFalse(a.has_trait('g'))
 
     def test_trait_metadata(self):
         class A(HasTraits):

traitlets/traitlets.py

@@ -689,7 +689,6 @@ def _notify_trait(self, name, old_value, new_value):
                 raise TraitError('a trait changed callback '
                                     'must be callable.')
 
-
     def _add_notifiers(self, handler, name):
         if name not in self._trait_notifiers:
             nlist = []
@@ -801,6 +800,10 @@ def class_own_traits(cls, **metadata):
         return {n: t for (n, t) in cls.class_traits(**metadata).items()
                 if getattr(sup, n, None) is not t}
 
+    def has_trait(self, name):
+        """Returns True if the object has a trait with the specified name."""
+        return isinstance(getattr(self.__class__, name, None), TraitType)
+
     def trait_names(self, **metadata):
         """Get a list of all the names of this class' traits."""
         return self.traits(**metadata).keys()