[Python-Dev] Re: pickle me, Elmo? (weakref feature request)

[Guido van Rossum]

> Is this the right time to post a feature request ?

To get something into Python 2.3's pickling, it's now or never.

> It's about pickling weakrefs:
> 
> let's assume i 've created 3 class instances
> 
> >>> class A:
> ...     pass
> 
> >>> a = A()
> >>> b = A()
> >>> c = A()
> >>> a.b = b                  #put b into a
> >>> a.ref_b = weakref.ref(b) #weakref to b
> >>> a.ref_c = weakref.ref(c) #weakref to c
> 
> now i pickle around
> 
> >>> data = pickle.dumps(a)
> >>> new_a = pickle.loads(data)
> 
> now i would like to have:
> 
> new_a       is my unpickled a
> new_a.b     is my unpickled b
> new_a.ref_b is an weakref to new_a.b
> new_a.ref_c is an dead weakref 
> (c was not pickled because it's just weakly-referenced)
> 
> 
> weakrefs are not supported by the default, but this kind of 'support' 
> could not (i didn't get it ;) be added using the  copy_reg module,
> but it seems to be very useful;

Your grammar here seems garbled; I'll just take it to mean that you'd
like the example to work. ;-)

> weakrefs could used as an "pickling-barrier"...
> 
> what do you think?

I brainstormed for a few minutes with Fred Drake, the weakref expert,
but we saw many obstacles to implementing it.  It would be A Major
Project to implement this: it would require adding new methods to
weakref objects, and new pickling codes, and an extension to the
pickling and unpickling engines...

IOW, I don't see it happening.

--Guido van Rossum (home page: http://www.python.org/~guido/)