WANTED: example programs with cycles

[Guido van Rossum]

We're experimenting with forms of garbage collection that works nicely
with reference counts and still collects cycles.

In order to exercise this code, I'm looking for representative
real-world Python code that creates cyclic data structures that are
currently not collected by Python's reference-counting garbage
collector.  I'm not looking for programs that grow as a result of a
reference counting bug in the interpreter -- the new collector won't
find those either.  I'd like the programs to be reasonably
self-contained: no 3rd party extensions modules, no GUI usage except
maybe Tkinter, no network I/O, no 3rd party code except your own code.
(These are not restrictions of the garbage collector, just
requirements to make it easy for me to run the test programs.)  A few
modules, a main script, and an input data file would be great.  It
also helps if I can somehow tell whether the program does the right
thing by comparing its output to some reference output.

Mail your code (or pointers to webpages with your code) to
guido at python.org.  Make sure that the subject looks like a reply to
this message.

(Don't ask for patches yet -- the code will be released through the
CVS tree if and when it's ready.  If it works well enough, it will
become part of Python 1.6 -- possibly as a compile-time or run-time
option.)

Thanks!

--Guido van Rossum (home page: http://www.python.org/~guido/)