exar...@twistedmatrix.com wrote: > On 02:48 pm, m...@egenix.com wrote: >> exar...@twistedmatrix.com wrote: >>> On 03:17 pm, pengyu...@gmail.com wrote: >>>> Hi, >>>> >>>> If I define my own class and use pickle to serialize the objects in >>>> this class, will the serialized object be successfully read in later >>>> version of python. >>>> >>>> What if I serialize (using pickle) an object of a class defined in >>>> python library, will it be successfully read in later version of >>>> python? >>> >>> Sometimes. Sometimes not. Python doesn't really offer any guarantees >>> regarding this. >> >> I think this needs to be corrected: the pickle protocol versions are >> compatible between Python releases, however, there are two things to >> consider: >> >> * The default pickle version sometimes changes between minor >> releases. >> >> This is easy to handle, though, since you can provide the pickle >> protocol version as parameter. >> >> * The pickle protocol has changed a bit between 2.x and 3.x. >> >> This is mostly due to the fact that Python's native string >> format changed to Unicode in 3.x. > > The pickle protocol isn't the only thing that determines whether an > existing pickle can be loaded. Consider this very simple example of a > class which might exist in Python 2.x: > > [...changes to baseclasses and __init__ arguments...] > > So these are the kinds of things I am talking about when I say that > there aren't really any guarantees.
True, there's no guarantee that pickle can work out your code changes. I think that's a bit much to expect from a serialization protocol :-) I was only talking about the data storage format itself, ie. whether it's possible to pickle the data in Python 2.n and load it again in 2.n+m without code changes. Even with code changes, you can still work-around many issues by implementing a proper .__setstate__() method in your class and using a class .version attribute to detect older pickles. -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Oct 13 2009) >>> Python/Zope Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ ::: Try our new mxODBC.Connect Python Database Interface for free ! :::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ -- http://mail.python.org/mailman/listinfo/python-list
