well, the title says "CGI-base", but the post says "eventually Tk as well"... and this bringsup an fascinating point.

How to make portable sessioning code? because if you were in mod_perl, I'd say Apache::Session, but then outside of mod_perl, well I dont really know. The Stein/maceachern book on mod_perl lists a total of 6 ways of doing this, but I can't imagine any of them appplying to Tk... as state is usually resident within the single process that a Tk program runs in.