cPickle - sharing pickled objects between scripts and imports

[Peter Otten]

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.