Usage Example for Persistent_Id and Persistent_Load of Pickle

[Dana Heins]

I'm looking for some real-life examples of how to use persistent_id and
persistent_load of pickle.  I am trying to store object instances in pickle
which share object instances in multiple files.  The examples that I've
found so far don't really help, any pointers would be greatly appreciated.

For example:

I have classes a, b and c and b and c each contain references to class a.
All three are pickled into seperate files, how do I reload classes b and c
so they share the same reference to a?

THanks!