Re: How to pickle bound methods

[srinivasan srinivas]

Peter,
Could you please explain the code breifly?? I am not getting what it does.
Thanks,
Srini 



----- Original Message ----
From: Peter Otten <__peter__@web. de>
To: python-list@python.org
Sent: Wednesday, 2 July, 2008 12:53:19 PM
Subject: Re: How to pickle bound methods

srinivasan srinivas wrote:

I would like to know how to pickle a bound method??

$ cat pickle_method.p y
import copy_reg
import new

def make_instanceme thod(inst, methodname):
    return getattr(inst, methodname)

def pickle_instance method(method):
    returnmake_inst ancemethod, (method.im_self , method.im_func. __name__)

copy_reg.pickle (new.instanceme thod, pickle_instance method,
make_instanceme thod)

if __name__ == "__main__":
    import pickle

    class A(object):
        def __init__(self, who):
            self.who = who
        def alpha(self):
            print "Hello,", self.who


    FILENAME = "method.pic kle"

    import sys
    args = sys.argv[1:]
    if args:
        a = A(args[0])
        m = a.alpha
        pickle.dump(m, open(FILENAME, "wb"))
    else:
        m = pickle.load(ope n(FILENAME, "rb"))
        m()

$ python pickle_method.p y world
$ python pickle_method.p y
Hello, world
$ python pickle_method.p y Srini
$ python pickle_method.p y
Hello, Srini

Peter
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[Peter Otten]

Re: How to pickle bound methods

srinivasan srinivas wrote:

Please don't top-post.

Could you please explain the code breifly?? I am not getting what it does.

>import copy_reg
>import new
>>
>def make_instanceme thod(inst, methodname):
>    return getattr(inst, methodname)
>>
>def pickle_instance method(method):
>    return make_instanceme thod, (method.im_self , method.im_func. __name__)
>>
>copy_reg.pickl e(new.instancem ethod, pickle_instance method,
>make_instancem ethod)

If you have a type that cannot be pickled because it is implemented in C you
can make it "picklable" by registering it with the copy_reg.pickle ()
function. This function takes three arguments:

1 the type (here: new.instancemet hod)
2 a function that takes an instance of the type. This returns a factory
function and a tuple of the arguments this factory function needs to
recreate the instance.
3 the factory function.

In short the following must work, and out_method should do the same thing as
in_method:

factory, args = pickle_instance method(in_metho d)
out_method = factory(*args)

Now to your other problem, pickling static methods. The type of a static
method is just new.function, the same as that of a global function. Global
functions are already picklable, so the copy_reg mechanism doesn't kick in.

Peter