On Tue, Mar 13, 2012 at 2:50 PM, Merlijn van Deen <valhall...@arctus.nl> wrote: > On 13 March 2012 22:13, Guido van Rossum <gu...@python.org> wrote: >> Well, since trying to migrate data between versions using pickle is >> the "wrong" thing anyway, I think the status quo is just fine. >> Developers doing the "right" thing don't use pickle for this purpose. > > I'm confused by this. "The pickle serialization format is guaranteed > to be backwards compatible across Python releases" [1], which - at > least to me - suggests it's fine to use pickle for long-term storage, > and that reading this data in new Python versions is not a "bad" > thing to do. Am I missing something here? > > [1] http://docs.python.org/library/pickle.html#the-pickle-protocol
That was probably written before Python 3. Python 3 also dropped the long-term backwards compatibilities for the language and stdlib. I am certainly fine with adding a warning to the docs that this guarantee does not apply to the Python 2/3 boundary. But I don't think we should map 8-bit str instances from Python 2 to bytes in Python 3. My snipe was mostly in reference to the many other things that can go wrong with pickled data as your environment evolves -- if you're not careful you can have references (by name) to modules, functions, classes in pickled data that won't resolve in a later (or earlier!) version of your app, or you might have objects that are unpickled in an incomplete state that causes later use of the objects to break (e.g. if a newer version of __init__() sets some extra instance variables -- unpickling doesn't generally call __init__, so these new variables won't be set if they didn't exist in the old version). Etc., etc. If you can solve your problem with a suitably hacked Unpickler subclass that's fine with me, but I would personally use this opportunity to change the app to some other serialization format that is perhaps less general but more robust than pickle. I've been bitten by too many pickle-related problems to recommend pickle to anyone... -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
