Python 3000 (a.k.a. “Py3k”, and released as Python 3.0) is a new
version of the language that is incompatible with the 2.x line of
releases. The language is mostly the same, but many details, especially
how built-in objects like dictionaries and strings work, have changed
considerably, and a lot of deprecated features have finally been
removed.
This is an ongoing project; the cleanup isn’t expected to be
complete until 2008. In particular there are plans to reorganize the
standard library namespace.
The release plan is to have a series of alpha releases in 2007, beta
releases in 2008, and a final release in August 2008. The alpha
releases are primarily aimed at developers who want a sneak peek at the
new langauge, especially those folks who plan to port their code to
Python 3000. The hope is that by the time of the final release, many
3rd party packages will already be available in a 3.0-compatible form.
from: http://www.python.org/