'Because Libraries are XBlocks, they aren\'t exported in the same way Course Modules
are, but instead use the standard XBlock serializers. Accordingly, we need to
create our own index file to act as the equivalent to the root course.xml file,
called library.xml.'

def post_process(self, root, export_fs):

    xml_file = export_fs.open(LIBRARY_ROOT, 'w')
    xml_file.write(lxml.etree.tostring(root, pretty_print=True, encoding='utf-8'))
    xml_file.close()
