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Newsgroups: comp.lang.python
Date: Tue, 3 Apr 2012 07:29:31 -0700 (PDT)
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Subject: Re: why can't I pickle a class containing this dispatch dictionary?
From: 88888 Dihedral <dihedral88888@googlemail.com>
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Xref: csiph.com comp.lang.python:22597

Peter Otten=E6=96=BC 2012=E5=B9=B44=E6=9C=883=E6=97=A5=E6=98=9F=E6=9C=9F=E4=
=BA=8CUTC+8=E4=B8=8B=E5=8D=883=E6=99=8254=E5=88=8650=E7=A7=92=E5=AF=AB=E9=
=81=93=EF=BC=9A
> jkn wrote:
>=20
> >     I'm clearly not understanding the 'can't pickle instancemethod
> > objects' error; can someone help me to understand,=20
>=20
> I think classes implemented in C need some extra work to make them=20
> picklable, and that hasn't been done for instance methods.
>=20
> > & maybe suggest a
> > workaround, (apart from the obvious if ... elif...).
>=20
> You can implement pickling yourself:
>=20
> import copy_reg=20
> import types
>=20
> def pickle_instancemethod(m):
>     return unpickle_instancemethod, (m.im_func.__name__, m.im_self,=20
> m.im_class)=20
> =20
> def unpickle_instancemethod(name, im_self, im_class):
>     im_func =3D getattr(im_class, name)
>     return im_func.__get__(im_self, im_class)=20
> =20
> copy_reg.pickle(types.MethodType, pickle_instancemethod)=20
>=20
> =20
> > I'm running Python 2.6 on an embedded system.
> >=20
> > =3D=3D testpickle.py =3D=3D
> > import pickle
> >=20
> > class Test(object):
> >     def __init__(self):
> >         self.myDict =3D {
> >             1: self.tag1,
> >             2: self.tag2
> >             }
> >     def dispatch(self, v):
> >         try:
> >             self.myDict[v]()
> >         except KeyError:
> >             print "No corresponding dictionary entry!"
> >         #
> >     def tag1(self):
> >         print "one"
> >     def tag2(self):
> >         print "two"
> >=20
> >=20
> > t =3D Test()
> > t.dispatch(1)
> > t.dispatch(2)
> > t.dispatch(0)
> >=20
> > fd =3D open("pickle.out", "w")
> > pickle.dump(t, fd)
> > fd.close()
> > # EOF
> >=20
> > $ python testpickle.py
> > one
> > two
> > No corresponding dictionary entry!
>=20
> > TypeError: can't pickle instancemethod objects
> > $

Save your python files as a package in .pyd or .py  and use exec to get wha=
t you want. Of course you can use the data compression package to perform=
=20
serialization operations, but that will increase start up time in loading y=
our objects.