python2.7 -> 2.6 on mac

$ man python
$ which python
/usr/bin/python
$ python -V
Python 2.7.1
#
# temporarily change version
#
$ export VERSIONER_PYTHON_VERSION=2.6
$ python -V
Python 2.6.7
$ unset VERSIONER_PYTHON_VERSION
$ python -V
Python 2.7.1
#
# persistently change version
#
$ defaults write com.apple.versioner.python Version 2.6
$ python -V
Python 2.6.7