Re: [Pyobjc-dev] NSCoding support for python list & dict

[Barry W. <bar...@gm...>]

I don't think I have the chops to pull off the pickling of Objective-C
objects. It seems that we might be able to encode list and dict types
however by just calling [super encode...] from their OC_PythonXX
wrappers. Unless one of the gurus thinks that's a stupid idea, I will
give it a try.

Barry

On 11/27/07, Ronald Oussoren <ron...@ma...> wrote:
>
> On Tuesday, November 27, 2007, at 08:56AM, "Bill Bumgarner" <bb...@ma...> wrote:
> >On Nov 26, 2007, at 9:59 PM, Ronald Oussoren wrote:
> >> NSCoding support for other objects should also be doable, but is
> >> more work and requires a lot of testing. Pickling Objective-C
> >> objects on the other hand has the outlooks of being a very hard
> >> problem.
> >
> >NSArchiver and NSKeyedArchiver support arbitrary archival of objects.
> >That is, you can create an archiving session and then archive the sub-
> >graphs of objects of objects in arbitrary order and with arbitrary
> >references between the subgraphs.
> >
> >Pickling of a graph containing a mix of Python and Objective-C objects
> >could be done by creating a UUID for each object in the graph at the
> >pickle/archiver boundary.  The UUID could be stored in the pickle,
> >could be used to archive the sub-graph of Objective-C objects and
> >store 'em away via -encodeObject:forKey:, and then the resulting BLOB
> >of archived Objective-C data could be stored in the pickle as a
> ><string>.
> >
> >Completely trivial, right?
>
> At first glance that doesn't quite fit into the pickle interface, but could be made to work using a class/function on top of pickle that does the work.
>
> Dealing with cycles and object-identity will be interesting though (e.g. pickle.dumps([O, NSArray.arrayWithArray_([O])]), where O is a pure Python object (or even (O=[]; A=NSArray.arrayWithArray_([O]); O.append(A); pickle.dumps([O,A]).
>
> The other way around (adding NSCoding support to Python objects) is easy: just call __getstate__/__reduce__ to get object state, then use encodeObject:forKey: to write that, more basic, object to the stream.
>
> >
> >Only because of my ignorance.   There is a definite chicken-and-egg
> >problem in that archival will produce the archived obj-c objects
> >*last* whereas unarchival will need them to be decoded *first*.   And
> >that is just scratching the surface.
>
> What might work: implement __reduce__ for objc.objc_object using a custom NSCoder subclass that builds a python datastructure containing the object state, then let the pickle machinery serialize that. That is, encodeObject:forKey: would add the object to a dictionary. At some point the object state must be some basic object, such as C integers, which pickle can encode without further recursion.
>
> I know this is a bit vague, I made this up while typing this e-mail. It does look like something that can be made to work though.
>
> Volunteers?
>
> Ronald
> >
> >b.bum
> >
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