Create _attr/_attrNS lazily.
diff --git a/Lib/xml/dom/expatbuilder.py b/Lib/xml/dom/expatbuilder.py
index b4b28e4..ff9c1f1 100644
--- a/Lib/xml/dom/expatbuilder.py
+++ b/Lib/xml/dom/expatbuilder.py
@@ -760,6 +760,7 @@
             del self._ns_ordered_prefixes[:]
 
         if attributes:
+            node._ensure_attributes()
             _attrs = node._attrs
             _attrsNS = node._attrsNS
             for i in range(0, len(attributes), 2):