On Sun, 2006-06-18 at 15:38 +1000, John Pye wrote: > FWIW I found that I was able to pickle C++ objects but simply adding > python methods __reduce__ and __setstate__ in my SWIG .i file -- I'm not > sure if Matplotlib uses this approach or not. I didn't need to use > copy_reg (perhaps it's preferable? I don't know)
MPL uses CXX instead of SWIG; I'm no C++ export so I havn't looked at adding __get/setstate__ functions to the objects themselves. copy_reg is nice because you can add pickle-ability without modifying any matplotlib code. I've hit another potential problem though: it's not possible to access the full internal state of these objects from their python API, meaning they can't be stored this way. It looks like I need to understand the Figure creation process in a bit more detail. BC > > http://freesteam.cvs.sourceforge.net/freesteam/freesteam/freesteam.i?revision=1.16&view=markup > (this is from the steam properties project that I run, > http://freesteam.sf.net/) > > Cheers > JP > > Bryan Cole wrote: > > >On Sun, 2006-06-18 at 00:05 +1000, John Pye wrote: > > > > > >>Hi all, > >> > >>A thought just occurred to me: I wonder if it would be useful to be able > >>to 'pickle' Matplotlib plots, using the python cPickle library. This > >>way, I could save my plots in a form that would allow me to load them > >>back later (with just the necessary source data) and fiddle with things > >>like titles and legends and so on. Would be useful perhaps in the > >>context of preparing diagrams for an article or report. > >> > >>Has anyone tried this? Would it be recommended/not recommended/not even > >>possible? > >> > >> > > > >I had a look at this a while back. It looks like the well thought out > >structure of MPL should make this easy, although it would require a few > >adjustments. To make a Figure object pickle-able, all the internal > >objects in a Figure must also be pickle-able. Most of the innards of a > >Figure are python objects which should pickle without problem. The only > >parts which aren't are the "BinOps". These are custom C-coded objects > >which implement 'lazy evaluation' of the transformation expressions. > >They're defined in the _transforms.cxx/h files. > > > >In theory, you can easily make these C-objects pickle-able using the > >'copy_reg' module; you just register two functions, one to extracts the > >object's state as a pickle-able object, the other to construct a new > >instance of the object, initialised with the previously stored state. > > > >However, I ran into a problem: there's some bug in either python or CXX > >(the automatic C++ class wrapper which mpl uses for the compiled > >components) which results in a segfault when I tried pickling copy_reg > >enhanced BinOps. The templating techniques used by CXX are completely > >beyond me so this is where things have stuck. > > > >... but ... I just now tested this again with python-2.4.2 and > >mpl-0.87.2 and it works! yeay. Thus, if every object in > >matplotlib._transforms gets given a python reduction/construction > >function pair and registers them with copy_reg, this *should* be enough > >to make a Figure pickle-able. Unless I've missed something else... > > > >I may try this out later this week, unless someone else tries it first. > > > >Bryan > > > >PS. copy_reg example follows >>> > > > >import cPickle as pickle > >import copy_reg > > > >#let's test this on a simple 'Value' BinOp > >from matplotlib._transforms import Value > > > >def fcon(val): > > #constructor > > return Value(val) > > > >def fred(o): > > #reduction functions > > val = o.get() > > return fcon, (val,) > > > >#my starting object > >a=Value(5) > >print a, a.get() > > > >copy_reg.pickle(type(a), fred) > > > >data = pickle.dumps(a) > > > >new = pickle.loads(data) > >print "new", new, new.get() > > > > > > > >>Cheers > >>JP > >> > >> > > > > > > > > > >_______________________________________________ > >Matplotlib-users mailing list > >Matplotlib-users@lists.sourceforge.net > >https://lists.sourceforge.net/lists/listinfo/matplotlib-users > > > > > > _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
