Gracefully handle UnicodeEncodeError on python 2.

This can be produced when doing an attribute lookup. Turn it into a
LocationError (or the default value).

zope.container.traversal.ContainerTraversable was doing this already,
see https://github.com/zopefoundation/zope.container/blob/master/src/zope/container/traversal.py#L105

CHANGES.rst

@@ -8,6 +8,8 @@ Changes
 
 - Drop support for Python 2.6.
 
+- Gracefully handle ``UnicodeEncodeError`` that can be produced when
+  doing attribute lookup on Python 2 by instead raising a ``LocationError``.
 
 4.0.0 (2014-03-21)
 ------------------
@@ -283,4 +285,3 @@ No further changes since 3.4.0a1.
 
 Initial release as a separate project, corresponds to ``zope.traversing``
 from Zope 3.4.0a1
-

src/zope/traversing/adapters.py

@@ -38,7 +38,14 @@ def __init__(self, subject):
     def traverse(self, name, furtherPath):
         subject = self._subject
         __traceback_info__ = (subject, name, furtherPath)
-        attr = getattr(subject, name, _marker)
+        try:
+            attr = getattr(subject, name, _marker)
+        except UnicodeEncodeError:
+            # If we're on Python 2, and name was a unicode string the
+            # name would have been encoded using the system encoding
+            # (usually ascii). Failure to encode means invalid
+            # attribute name.
+            attr = _marker
         if attr is not _marker:
             return attr
         if hasattr(subject, '__getitem__'):
@@ -133,6 +140,14 @@ def traversePathElement(obj, name, further_path, default=_marker,
 
     try:
         return traversable.traverse(nm, further_path)
+    except UnicodeEncodeError:
+        # If we're on Python 2, and nm was a unicode string, and the traversable
+        # tried to do an attribute lookup, the nm would have been encoded using the
+        # system encoding (usually ascii). Failure to encode means invalid attribute
+        # name.
+        if default is not _marker:
+            return default
+        raise LocationError(obj, name)
     except LocationError:
         if default is not _marker:
             return default

src/zope/traversing/tests/test_conveniencefunctions.py

@@ -118,6 +118,23 @@ def testTraverseNameBadValue(self):
             self.folder, './item'
             )
 
+    def testTraverseNameUnicode(self):
+        from zope.traversing.api import traverseName
+        from zope.interface import implementer
+
+        @implementer(ITraversable)
+        class BrokenTraversable(object):
+            def traverse(self, name, furtherPath):
+                getattr(self, u'\u2019', None)
+                # The above actually works on Python 3
+                raise LocationError()
+
+        self.assertRaises(
+            LocationError,
+            traverseName,
+            BrokenTraversable(), '')
+
+
     def testGetName(self):
         from zope.traversing.api import getName
         self.assertEqual(

src/zope/traversing/tests/test_traverser.py

@@ -271,6 +271,10 @@ def testNotFound(self):
 
         self.assertRaises(LocationError, df.traverse, 'bar', [])
 
+    def testUnicodeTraversal(self):
+        df = DefaultTraversable(object())
+        self.assertRaises(LocationError, df.traverse, u'\u2019', ())
+
 def test_suite():
     loader = unittest.TestLoader()
     suite = loader.loadTestsFromTestCase(TraverserTests)