Python 1.6 was the last of the versions developed at CNRI and the only version issued by CNRI with an open source license. Following the release of Python 1.6, and after Guido van Rossum left CNRI to work with commercial software developers, it became clear that the ability to use Python with software available under the GNU General Public License (GPL) was very desirable. CNRI and the Free Software Foundation (FSF) interacted to develop enabling wording changes to the Python license. Python 1.6.1 is essentially the same as Python 1.6, with a few minor bug fixes, and with a GPL-compatible license.

Python 1.6.1
http://www.python.org/download/releases/1.6.1/