n Tue, Jul 20, 2010 at 8:27 AM, Nick Coghlan <ncoghlan@gmail.com> wrote:
For the record, I am personally +1 on the idea (otherwise I wouldn't
have put so much thought into it over the years). It's just a *lot*
harder to define complete and consistent semantics for the concept
than people often realise.

However, having the question come up twice within the last month
finally inspired me to write the current status of the topic down in a
deferred PEP: http://www.python.org/dev/peps/pep-3150/

There was a related discussion on python-ideas in July 2009, spanning two threads, that you may want to additionally reference.  A lot of corner cases were also brought up in that thread.

Here are the starts of the two threads:

Daniel Stutzbach, Ph.D.
President, Stutzbach Enterprises, LLC