The module documentation recommends...

More picklability

Ensure that all arguments to Process.__init__() are picklable. This means, in particular, that bound or unbound methods cannot be used directly as the target (unless you use the fork start method) — just define a function and use that instead.

...but methods (bound and unbound) are now pickleable (given their self.object is picklable).

Patch attached. I also checked that this case is tested, and it looks like the Bunch object in Lib/test/_test_multiprocessing.py uses a method as its target.

Thanks for the Rietveld comments. I have attached a new patch.

Actually, we can remove the versionchanged directive. The attached script works fine with the spawn start method in Python 3.4.

I will commit the following version:

    Ensure that all arguments to :meth:`Process.__init__` are picklable.
    Also, if you subclass :class:`~multiprocessing.Process` then make sure that
    instances will be picklable when the :meth:`Process.start
    <multiprocessing.Process.start>` method is called.

New changeset 97254031f0b7 by Berker Peksag in branch '3.5':
Issue #27221: Delete an outdated paragraph about pickle support of Process
https://hg.python.org/cpython/rev/97254031f0b7

New changeset 5b9d8b5b1139 by Berker Peksag in branch 'default':
Issue #27221: Merge from 3.5
https://hg.python.org/cpython/rev/5b9d8b5b1139

Thanks!