The DOM has (atleast in level 2) an interface DATASection, and an operation Document::createCDATASection. They are extension interfaces, supported only if an implementation supports the "xml" feature.
from xml.dom import minidom
my_xmldoc=minidom.parse(xmlfile)
my_xmldoc.createCDATASection(data)
now u have cadata node add it wherever u want....
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