The most important thing to remember about dealing with XML Namespaces in Python code is the convention that empty namespaces and prefixes are marked by None, not "". Actually, it's best that you use the symbols xml.dom.EMPTY_NAMESPACE and xml.dom.EMPTY_PREFIX in PyXML 0.8.2. This is a cause of a huge number of misunderstandings, so I'll repeat.
To represent the empty namespace, use the symbol xml.dom.EMPTY_NAMESPACE. o represent the empty prefix, use xml.dom.EMPTY_PREFIX.
Here are some examples of threads where this confusion has come up: