How can I write structured data to a file and then read it back into the same structure later?

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Why not use python pickle?
Python has a great serializing module called pickle it is very easy to use.

import cPickle
cPickle.dump(obj, open('save.p', 'wb')) 
obj = cPickle.load(open('save.p', 'rb'))

There are two disadvantages with pickle:

  • It’s not secure against erroneous or
    maliciously constructed data. Never
    unpickle data received from an
    untrusted or unauthenticated source.
  • The format is not human readable.

If you are using python 2.6 there is a builtin module called json. It is as easy as pickle to use:

import json
encoded = json.dumps(obj)
obj = json.loads(encoded)

Json format is human readable and is very similar to the dictionary string representation in python. And doesn’t have any security issues like pickle. But might be slower than cPickle.

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