Some hours ago I sent an email to python-crypto asking how to securely wipe cryptographic secrets from memory: http://mail.python.org/pipermail/python-crypto/2013-February/001170.html
Antoine said that cryptographic secret wiping could be achieved if one uses bytearrays carefully and then overwrites their contents after use. I agree that this sounds reasonable, but I think it would be even better if that was a documented property of bytearrays.
That might work if you never ever resize a bytearray during its life cycle. A resize op calls realloc() which may copy the data to a new memory region. The old region isn't zeroed. The approach only takes care of the object itself on the heap. Some function may store data on the stack or make a temporary copy to another memory location on the heap. You have to compensate for that. libtomcrypt has a function burn_stack() that allocates and overwrites memory on the stack with a recursive function call. Christian