why can't I pickle a class containing this dispatch dictionary?
Peter Otten
__peter__ at web.de
Tue Apr 3 03:54:50 EDT 2012
jkn wrote:
> I'm clearly not understanding the 'can't pickle instancemethod
> objects' error; can someone help me to understand,
I think classes implemented in C need some extra work to make them
picklable, and that hasn't been done for instance methods.
> & maybe suggest a
> workaround, (apart from the obvious if ... elif...).
You can implement pickling yourself:
import copy_reg
import types
def pickle_instancemethod(m):
return unpickle_instancemethod, (m.im_func.__name__, m.im_self,
m.im_class)
def unpickle_instancemethod(name, im_self, im_class):
im_func = getattr(im_class, name)
return im_func.__get__(im_self, im_class)
copy_reg.pickle(types.MethodType, pickle_instancemethod)
> I'm running Python 2.6 on an embedded system.
>
> == testpickle.py ==
> import pickle
>
> class Test(object):
> def __init__(self):
> self.myDict = {
> 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"
>
>
> t = Test()
> t.dispatch(1)
> t.dispatch(2)
> t.dispatch(0)
>
> fd = open("pickle.out", "w")
> pickle.dump(t, fd)
> fd.close()
> # EOF
>
> $ python testpickle.py
> one
> two
> No corresponding dictionary entry!
> TypeError: can't pickle instancemethod objects
> $
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