builder = ElementMaker(namespace='http://a.different.url/blah/v.10', nsmap=
    {'adlcp': 'http://a.namespace.url/blah/v.10', 'anotherns':
    'http://a.different.url/blah/v.10'})
builder.resource()
builder.attrib['href'] = 'Unit 4.html'
How to add a namespace to an attribute in lxml