Try this: Open file. Read file. Calculate MD5sum If md5 has changed, reparse the file. If not, show a cached tree. You'll have to come up with your own method for caching the tree.

Troy

Woa, fast answer, thanks Troy, but I fear I wasn't clear enough. I have no problem figuring out when to cache (I leech the flat file from a server). I don't know how to store an object tree from an external method like I would do with pickle/cpickle in pure python. cheers, oliver