Overload __or__ on traitlets and add a test

IPython/utils/tests/test_traitlets.py

@@ -16,7 +16,7 b' import nose.tools as nt'
 from nose import SkipTest
 
 from IPython.utils.traitlets import (
-    HasTraits, MetaHasTraits, TraitType, Any, CBytes, Dict,
+    HasTraits, MetaHasTraits, TraitType, Any, Bool, CBytes, Dict,
     Int, Long, Integer, Float, Complex, Bytes, Unicode, TraitError,
     Union, Undefined, Type, This, Instance, TCPAddress, List, Tuple,
     ObjectName, DottedObjectName, CRegExp, link, directional_link,
@@ -762,13 +762,22 b' class AnyTraitTest(TraitTestBase):'
 
 class UnionTrait(HasTraits):
 
-    value = Union([Type(), Unicode()])
+    value = Union([Type(), Bool()])
 
 class UnionTraitTest(TraitTestBase):
 
-    obj = UnionTrait()
-    _default_value = None
-    _good_values = [int, float, 'ten']
+    obj = UnionTrait(value='IPython.utils.ipstruct.Struct')
+    _good_values = [int, float, True]
+    _bad_values = [[], (0,), 1j]
+
+class OrTrait(HasTraits):
+
+    value = Bool() | Unicode()
+
+class OrTraitTest(TraitTestBase):
+
+    obj = OrTrait()
+    _good_values = [True, False, 'ten']
     _bad_values = [[], (0,), 1j]
 
 class IntTrait(HasTraits):

IPython/utils/traitlets.py

@@ -445,6 +445,12 b' class TraitType(object):'
         else:
             return value
 
+    def __or__(self, other):
+        if isinstance(other, Union):
+            return Union([self] + other.trait_types)
+        else:
+            return Union([self, other])
+
     def info(self):
         return self.info_text
 
@@ -1062,10 +1068,16 b' class Union(TraitType):'
         for trait_type in self.trait_types:
             try:
                 return trait_type._validate(obj, value)
-            except Exception:
+            except TraitError:
                 continue
         self.error(obj, value)
 
+    def __or__(self, other):
+        if isinstance(other, Union):
+            return Union(self.trait_types + other.trait_types)
+        else:
+            return Union(self.trait_types + [other])
+
 #-----------------------------------------------------------------------------
 # Basic TraitTypes implementations/subclasses
 #-----------------------------------------------------------------------------