Unpickling from strings

[Marcin Chady]

I have pickled an object into a string and saved it in an hidden HTML form
field, so that I can recover the state when the form is resubmitted.
However, when the form comes back and I try to unpickle my object I get an
error saying that the module in which the object's class was originally
defined is unknown, even though the CGI script which does the unpickling has
already imported the module!

Has anyone got an idea why it is?

Marcin