Many thanks for the responses I've received here to my question (below).
After reading the responses, I understand what the problem is much better. In
addition to the solutions mentioned in the responses, now that I understand the
problem I'll offer up my own solution. The following is an executable script
named pick1.py:
===============
import pickle
class A(object):
def __init__(self, x):
self.x = x
def writePickle():
import pick1
a5 = pick1.A(5)
f = open('pick1.pickle', 'wb')
pickle.dump(a5, f)
f.close()
writePickle() # The dumped pickle can be read by any other script.
================
That is, we need to do the pickling in a context where the module name for the
class is "pick1" rather than "__main__". The example above allows us to do that
without changing __name__ or doing anything else of that nature.
Thanks again!
Gary
> When you define a class in a script, and then pickle instances of
> that class in the same script and store them to disk, you can't load
> that pickle in another script. At least not the straightforward way
> [pickle.load(file('somefile.pickle'))]. If you try it, you get an
> AttributeError during the unpickling operation.
>
> There is no problem, of course, if the class is defined in a module
> which is imported by the pickling script.
> pickle.load(file('somefile.pickle')) then works.
>
> Rather than provide specific examples here, there's a blog post from
> 2005 that discusses this issue in depth and presents the problem very
> well: http://stefaanlippens.net/pickleproblem. (I tested in Python
> 2.6 yesterday and the same issue persists.)
>
> Questions:
>
> 1) Does this have to be the case, or is it a design problem with
> pickles that should be remedied?
>
> 2) Is there an easier way around it than moving the class definition
> to a separate module? The blog post I point to above suggests putting
> "__module__ = os.path.splitext(os.path.basename(__file__))[0]" into
> the class definiton, but that's not working in my testing because
> when I do that, the pickling operation fails. Is there something else
> that can be done?
>
> This is obviously not a huge problem. Substantial classes should
> usually be defined in a separate module anyway. But sometimes it
> makes sense for a script to define a really simple, small class to
> hold some data, and needing to create a separate module just to
> contain such a class can be a little annoying.
--
Gary Robinson
CTO
Emergent Music, LLC
personal email: gary...@me.com
work email: grobin...@flyfi.com
Company: http://www.flyfi.com
Blog: http://www.garyrobinson.net
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