no need for union dynamic default

Author: rmorshea

.gitignore

@@ -17,3 +17,4 @@ __pycache__
 \#*#
 .#*
 .coverage
+.cache/v/cache/lastfailed

traitlets/tests/test_traitlets.py

@@ -1488,7 +1488,7 @@ class UnionListTrait(HasTraits):
 
     value = List(Int() | Bool())
 
-class TestUnionListTrait(HasTraits):
+class TestUnionListTrait(TraitTestBase):
 
     obj = UnionListTrait()
 

traitlets/traitlets.py

@@ -1820,15 +1820,6 @@ def __or__(self, other):
         else:
             return Union(self.trait_types + [other])
 
-    def make_dynamic_default(self):
-        if self.default_value is not Undefined:
-            return self.default_value
-        for trait_type in self.trait_types:
-            if trait_type.default_value is not Undefined:
-                return trait_type.default_value
-            elif hasattr(trait_type, 'make_dynamic_default'):
-                return trait_type.make_dynamic_default()
-
 
 #-----------------------------------------------------------------------------
 # Basic TraitTypes implementations/subclasses