I find myself wanting the newer version of python for development reasons and portability. To install the newer version of Python (3.3.0) in this case (substitute for whatever version you want), do the following from the Terminal.
wget http://python.org/ftp/python/3.3.0/Python-3.3.0.tgz && tar -xvf Python-3.3.0.tgz
cd Python-3.3.0
./configure
make
sudo make altinstall
To run the Python2.7 version, just type python at the shell prompt. To engage the new version.. type python3.3
Have fun
