We have some experience maintaining persistent object storage over long periods of time. The best solution we've found is to do something like this:
- create a read/write method on each class. Every class that needs to be stored must have this. This includes class you would store (eg Figure) and things that are member variables of those classes. - Each class stores a version number along with it's data which represents the version of the persistent representation for that class. So each class has its own, internal versioning scheme that represents a specific set of variables with specific types. - The read method on each class must check the version number and then read the appropriate data for that version of itself. Whenever the persistent representation of the class changes (usually if the member variables change), you increment the version number. Implicit in this is that if you change the member variables of a class, the class read method must be able to convert the variables that existed in the older version of itself into the new member variables (since that's what the new methods on that class will be using) FYI It is possible to use pickle to do this but you can't rely on pickle to automatically save the member dictionary. You need to implement __getstate__ and __setstate__ and have them incorporate a version number in the dictionary they return. In addition, you shouldn't blindly save every member variable. If member variables can be constructed in terms of other data, it may be better to store that data and then reconstruct the member variables in the __setstate__ method. Using this type of system, you get a hierarchy of objects that each have their own, internal versioning system. This lets you make changes to a single class, increment it's version, and update its save/load methods and it won't affect any other part of the system and still retains backwards reading capability. Ted > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Eric Firing > Sent: Tuesday, September 16, 2008 7:04 PM > To: John Hunter > Cc: Josef Koller; matplotlib-users@lists.sourceforge.net > Subject: Re: [Matplotlib-users] save or pickle figure object > > John Hunter wrote: > > On Tue, Sep 16, 2008 at 5:06 PM, Josef Koller <[EMAIL PROTECTED]> > wrote: > >> Hi folks, > >> I would like to save preliminary figures for later processing and > >> refinement with matplotlib. Is there a way to save or pickle a > figure > >> object and later reload it. Matlab has a feature like that and and I > was > >> wondering if matplotlib has it too. > > > > No, it doesn't exist. We've taken a stab at it once or twice, but > > have been stymied because we make extensive use of a python extension > > libray CXX, and these objects have resisted our attempts to pickle > > them. With our recent transforms refactoring, which removes the > > hairiest CXX dependency, it may be worth taking another look, but > > noone is currently working on it. > > My sense, based on very little experience, is that pickles of > complicated objects are very fragile, so even if we could pickle > figures, I fear it might cause more trouble ("I can't load this > absolutely critical figure I pickled 6 months ago") than it would be > worth. > > Eric > > ----------------------------------------------------------------------- > -- > This SF.Net email is sponsored by the Moblin Your Move Developer's > challenge > Build the coolest Linux based applications with Moblin SDK & win great > prizes > Grand prize is a trip for two to an Open Source event anywhere in the > world > http://moblin-contest.org/redirect.php?banner_id=100&url=/ > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/matplotlib-users > Checked by AVG - http://www.avg.com > Version: 8.0.169 / Virus Database: 270.6.21/1674 - Release Date: > 9/16/2008 8:15 AM ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
