Don't use string methods to allow sharing this code with PyXML.
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index b2b6e7d..3ed7236 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -391,7 +391,8 @@
         _write_data(writer, self.data)
 
 def _nssplit(qualifiedName):
-    fields = qualifiedName.split(':', 1)
+    import string
+    fields = string.split(qualifiedName,':', 1)
     if len(fields) == 2:
         return fields
     elif len(fields) == 1: