Specifying a module when Unpickling

[Markus Wankus]

Hi,

I was wondering what the *correct* way to do this would be...

I have a class, say Spam, which lives in a module Eggs.  My application 
uses binary pickles a its method of storing data in files.  So, in my 
application I pickle an instance of Spam, and all is well.

Now I have another application where I want to access teh data in this 
pickle.  However - I am including a version of the Eggs module in an 
installed package called Ham.  So, to use the module Eggs, I would now say:

from Ham import Eggs

mySpam = Eggs.Spam()

Fine.  Now - unpickling a Spam object will fail if the module Eggs is not 
importable in the current context.  I can see no way specifying to the 
unpickling mechanism a search path where to find the Eggs module.  How I 
was going to handle this was as follows:

In my Ham package, rename the Eggs.py to __Eggs__.py (just for fun), and 
have my function which does the unpickling do the following:

    from Ham import __Eggs__
    import cPickle

    need_restore = False
    if sys.modules.has_key('Eggs'):
        need_restore = True
        backup_key = sys.modules['Eggs']

    sys.modules['Eggs'] = sys.modules['Ham.__Eggs__']

    try:
        fo = file(r'some_filename', 'rb')
        mySpam = cPickle.Unpickler(fo).load()
        return mySpam
    finally:
        fo.close()
        if need_restore:
            sys.modules['Eggs'] = backup_key
        else:
            del sys.modules['Eggs']

This all seems to work great, but I was wondering if I have overlooked 
something.  Is there a way to tell the unpickler to use a certain module?  
Is what I have done above *bad* for any particular reason?

Any feedback would be welcome.
Thanks,

-- 
Markus