I love named tuples, they rock for this kind of task: storing complicated structure in a python compatible way, without too much hassle.
And as far as load/save on disk is concerned, I simply use regular python structure with safe eval [1]. I get all the flexibility that I need for the file format, without the annoyance of writing a conversion layer. [1]: http://code.activestate.com/recipes/364469-safe-eval/ -- http://mail.python.org/mailman/listinfo/python-list
