problem doing unpickle in an exec statement

castironpi castironpi at gmail.com
Thu Jul 24 06:07:33 CEST 2008


On Jul 23, 6:01 pm, Danny Shevitz <shev... at lanl.gov> wrote:
> Howdy,
>
> In my app I need to exec user text that defines a function. I want this
> function to unpickle an object. Pickle breaks because it is looking for
> the object definition that isn't in the calling namespace.
>
> I have mocked up a simple example that shows the problem. Run this
> first code (from create_pickle.py) to create the pickle.
>
> create_pickle.py: (run this first)
>
> #############################################
> import cPickle
>
> # the pickle file name
> file_name = 'd:\\temp\\test1.pickle'
>
> # define a class
> class Tree(object):
>         pass
>
> def main():
>         # instantiate  
>         t = Tree()
>
>         # create the sweet pickle
>         fp = open(file_name, 'wb')
>         cPickle.dump(t, fp)
>         fp.close()
>
>         # try to unpickle directly
>         fp = open(file_name, 'rb')
>         result = cPickle.load(fp)
>         fp.close()
>         print "unpickling directly works just fine, result = ", result
>
> if __name__=='__main__':
>         main()
> #############################################
>
> run this second:
>
> exec_pickle.py
> #############################################
> # this file shows a problem with sweet pickle in an exec statement
>
> # the pickle file name
> file_name = 'd:\\temp\\test1.pickle'
>
> # code to be turned into a function
> code_text = '''
> def include():
>   print "this works!"
> '''
>
> # a function for creating functions
> def create_fun(code_text):
>         clean_dict = {}
>         exec code_text in clean_dict
>         return clean_dict['include']
>
> # include_fun is a bona fide function
> include_fun = create_fun(code_text)
>
> # this works
> include_fun()
>
> # now try to load the pickle in an exec statement
> code_text = '''
> def include(file_name):
>   print "processing file_name: ", file_name
>   import cPickle
>   fp = open(file_name, "rb")
>   result = cPickle.load(fp)
>   fp.close()
>   print "result = ", result
> '''
>
> # create the new include_fun
> include_fun = create_fun(code_text)
>
> # run it
> include_fun(file_name)
>
> #############################################
>
> Can anyone enlighten me what I need to do to exec_pickle.py
> to get this to work?
>
> thanks,
> Danny

Hi,

It works if you paste

# define a class
class Tree(object):
        pass

into exec_pickle.py.  There are inherent dilemmas in pickling
instances of non-primitive types, such as definition location, and
change in definition across versions.  How does 'class Tree' fit in to
your design module?



More information about the Python-list mailing list