[C++-sig] Serialization/pickle

[David Abrahams]

The following message is a courtesy copy of an article
that has been posted to gmane.comp.lib.boost.user as well.

"Drumheller, Michael" <michael.drumheller at boeing.com> writes:

>>>  From: David Abrahams <dave <at> boost-consulting.com>
>>>  Subject: Re: Boost.python serialization
>>>  Newsgroups: gmane.comp.lib.boost.user
>>>  Date: 2005-11-29 23:28:17 GMT (6 days, 17 hours and 9 minutes ago)
>>>  
>>>  "Drumheller, Michael" <michael.drumheller <at> boeing.com> writes:
>>>  
>>>  > Thank you for the help.  I have seen that link (the one you supplied)
>>>  > before, but I posted my question because that link in particular does
>>>  > not mention the words "Boost.Serialization" or "Archive" at all.  
>>>  
>>>  That's because the Boost Serialization library is unrelated.
>
> I understand that it is technically unrelated.  I am asking for
> information about about patterns of actual usage.

I'm afraid I don't know that.

>>>  > I suppose what I was really getting at, and was probably not very
>>>  > clear about (sorry :| ) was whether the specific approach (by
>>>  > N. Becker) of using a stringstream wrapped with a
>>>  > boost::archive::binary_oarchive is a standard idiom.
>>>  
>>>  "Standard?"
>
> OK: "common," "popular," "preferred," "regarded-as-best-practice,"
> "effective."

Ditto.

>>>  > (Basically, I would have thought that "python pickle boost::archive"
>>>  > would be a million-hit Google query, but it's only about a dozen. I
>>>  > find that weird.  Do people just not serialize their C++ extensions
>>>  > very often?)
>>>  
>>>  Yes, they do it very often.  There's usually no need to touch
>>>  Boost.Serialization in order to do so, though.
>
> My extensions refer to one another, i.e., they form a significant object
> hierarchy in and of themselves.  E.g., on the C++ side I might have an
> instance x of class X, which contains a vector of shared_ptrs p1,...,pn
> to instances y1,...,yn of another C++ class Y.  At pickle-time there may
> be Python object z with a member u bound to to x and members w1,...,wm
> bound to a subset of the y1,...,yn.  Is it even feasible to expect to be
> able to simple pickle.dump z and have it all work?

Yes.  Of course you have to do some work in your wrapping code to say
how X gets pickled.

> Please keep in mind:  I am just getting started wading into serializing
> a pretty complicated set of strongly interdependent Python and C++
> objects and I am just trying to get my bearings.  If this is the wrong
> forum to be asking these questions, please tell me.

Well, the C++-sig _might_ be more appropriate:
http://www.boost.org/more/mailing_lists.htm#cplussig (cross-posted there)

We (Boost Consulting) are actually planning to do something like this
with one of our clients, but we haven't gotten started with it yet.  I
think everything should "just work" as long as you take care not to
try to serialize the same object both from the C++ side (using
Boost.Serialization) and from the Python side (using pickle).  Because
each system implements its own object tracking, you could end up
representing the same object twice.

HTH,

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com