Got your message before I got his.  Thanks for the reference to python-list.

-----Original Message-----
>From: "R. David Murray" <report@bugs.python.org>
>Sent: Nov 18, 2012 9:39 PM
>To: ttcooper@indy.net
>Subject: [issue16498] Unwanted link between volatile and shelve storage
>
>
>R. David Murray added the comment:
>
>If it "got it" from dBasis[163] via item assignment (say gList1[i1][1] = dBasis[163]), then yes, Python remembers that.  Names just hold pointers to objects, so after that assignment gList1[i1][1] points to the same object as dBasis[163] does.  If that object is mutable, and you mutate it (as += will do, if the object is mutable), both names will still reference the same object, the one that has been changed.  
>
>As Serhiy suggested, you are more likely to get help with this on python-list.
>
>----------
>
>_______________________________________
>Python tracker <report@bugs.python.org>
><http://bugs.python.org/issue16498>
>_______________________________________