Thanks to efforts of Mathieu Xhonneux, web.py is almost ready for Python 3.
I've merged the py3 branch where the development was going on and pushed a dev version to pypi.
You can install it using:
pip install web.py==0.40.dev0
Please test it with your applications and let me know if you find any issues.
There are a bunch of open issues tagged as "py3" in the issue tracker, you are welcome to work on them.