why can't I pickle a class containing this dispatch dictionary?

[88888 Dihedral]

Peter Otten於 2012年4月3日星期二UTC+8下午3時54分50秒寫道：
> 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
> > $

Save your python files as a package in .pyd or .py  and use exec to get what you want. Of course you can use the data compression package to perform 
serialization operations, but that will increase start up time in loading your objects.