cPickle - sharing pickled objects between scripts and imports

[Rotwang]

On 23/06/2012 17:13, Peter Otten wrote:
> Rotwang wrote:
>
>> Hi all, I have a module that saves and loads data using cPickle, and
>> I've encountered a problem. Sometimes I want to import the module and
>> use it in the interactive Python interpreter, whereas sometimes I want
>> to run it as a script. But objects that have been pickled by running the
>> module as a script can't be correctly unpickled by the imported module
>> and vice-versa, since how they get pickled depends on whether the
>> module's __name__ is '__main__' or 'mymodule' (say). I've tried to get
>> around this by adding the following to the module, before any calls to
>> cPickle.load:
>>
>> if __name__ == '__main__':
>>       import __main__
>>       def load(f):
>>           p = cPickle.Unpickler(f)
>>           def fg(m, c):
>>               if m == 'mymodule':
>>                   return getattr(__main__, c)
>>               else:
>>                   m = __import__(m, fromlist = [c])
>>                   return getattr(m, c)
>>           p.find_global = fg
>>           return p.load()
>> else:
>>       def load(f):
>>           p = cPickle.Unpickler(f)
>>           def fg(m, c):
>>               if m == '__main__':
>>                   return globals()[c]
>>               else:
>>                   m = __import__(m, fromlist = [c])
>>                   return getattr(m, c)
>>           p.find_global = fg
>>           return p.load()
>> cPickle.load = load
>> del load
>>
>>
>> It seems to work as far as I can tell, but I'll be grateful if anyone
>> knows of any circumstances where it would fail, or can suggest something
>> less hacky. Also, do cPickle.Pickler instances have some attribute
>> corresponding to find_global that lets one determine how instances get
>> pickled? I couldn't find anything about this in the docs.
>
> if __name__ == "__main__":
>      from mymodule import *
>
> But I think it would be cleaner to move the classes you want to pickle into
> another module and import that either from your main script or the
> interpreter. That may also spare you some fun with unexpected isinstance()
> results.

Thanks.

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