[Python-Dev] multiprocessing not compatible with functional.partial

[Hrvoje Niksic]

Calvin Spealman wrote:
> I don't think it would be unreasonable to consider either 1) making
> functools.partial picklable (I don't know how feasible this is)

It's not only feasible, but quite easy and, I think, useful.  A 
"partial" instance is a simple triplet of (function, args, kwds), and it 
can be pickled as such.  For example:

 >>> import copy_reg, functools
 >>> def _reconstruct_partial(f, args, kwds):
...     return functools.partial(f, *args, **(kwds or {}))
...
 >>> def _reduce_partial(p):
...     return _reconstruct_partial, (p.func, p.args, p.keywords)
...
 >>> copy_reg.pickle(functools.partial, _reduce_partial)

Test:

 >>> import operator, cPickle as cp
 >>> p = functools.partial(operator.add, 3)
 >>> p(10)
13
 >>> cp.dumps(p)
'c__main__\n_reconstruct_partial\np1\n(coperator\nadd\np2\n(I3\ntp3\nNtRp4\n.'
 >>> p2 = cp.loads(_)
 >>> p2(10)
13

Iedally this should be implemented in the functools.partial object itself.