Return always string as str and unicode as unicode.

codec used for encoding is utf-8.

src/xml_marshaller/xml_marshaller.py

@@ -440,14 +440,18 @@ class Unmarshaller(ElementTreeContentHandler):
 
   def um_end_string(self, name):
     ds = self.data_stack
-    # might need to convert unicode string to byte string
-    ds[-1] = unescape(''.join(ds[-1]))
+    value = unescape(''.join(ds[-1]))
+    if isinstance(value, unicode):
+      value = value.encode('utf-8')
+    ds[-1] = value
     self.accumulating_chars = 0
 
   def um_end_unicode(self, name):
     ds = self.data_stack
-    # might need to convert unicode string to byte string
-    ds[-1] = unescape(''.join(ds[-1]))
+    value = unescape(''.join(ds[-1]))
+    if not isinstance(value, unicode):
+      value = value.decode('utf-8')
+    ds[-1] = value
     self.accumulating_chars = 0
 
   def um_end_int(self, name):