fix the _namespace_map cleanup for cElementTree tests.

Lib/test/test_xml_etree.py

@@ -1881,12 +1881,7 @@ class CleanContext(object):
 
     def __enter__(self):
         from xml.etree import ElementPath
-        if hasattr(ET, '_namespace_map'):
-            self._nsmap = ET._namespace_map
-        else:
-            # when testing the cElementTree alias
-            from xml.etree.ElementTree import _namespace_map
-            self._nsmap = _namespace_map
+        self._nsmap = ET.register_namespace._namespace_map
         # Copy the default namespace mapping
         self._nsmap_copy = self._nsmap.copy()
         # Copy the path cache (should be empty)

Lib/xml/etree/ElementTree.py

@@ -1086,6 +1086,8 @@ _namespace_map = {
     # dublin core
     "http://purl.org/dc/elements/1.1/": "dc",
 }
+# For tests and troubleshooting
+register_namespace._namespace_map = _namespace_map
 
 def _raise_serialization_error(text):
     raise TypeError(