First you’ll want to download the current production version of Python.
This is the one I installed (Mac users: Look for “Mac OS” on the list on the download page):
Mac OS X 32-bit i386/PPC Installer (2.7.2) for Mac OS X 10.3 through 10.6  (sig)
There might be a different one by the time you read this. Of course, Windows users will install a Windows version.
HINT: Exit Python (Control-d) and quit Terminal before you do this!
Simply save the file, and then open the DMG* that has been downloaded. It installs like any other Mac software. It will create a folder named Python 2.7 inside your Applications folder.
COMPLETE THE INSTALLATION
"Double-click on the ‘Update Shell Profile’ command to add the ‘bin’ directory inside the framework to your shell’s search path." (This instruction is given in the ReadMe.txt file in the DMG. You didn’t read the Read Me file? Shame on you!)
To find this (Update Shell Profile), open your Applications folder (Mac OS), then open the Python 2.7 folder. You should see the “Update Shell Profile” command there. By doing this, you will ensure that your system “sees” this new version as the current version of Python that should be used.
The next time you open Terminal and type python, you should see the new version.
*A DMG is a normal Mac OS installer for programs and applications.