I was running:
Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.

I downloaded the msi for Python 2.7.12 and attempted to run it. During the installation it gave me the following error:

"There is a problem with this Windows Installer package. A program required for this install to complete could not be run. Contact your support personnel or package vendor."


Then it "rolls back" the action, which killed my current 2.7.11 installation.  Despite that it states: 

"Python 2.7.12 setup ended prematurely because of an error. Your system has not been modified. To install this program at a later time, please run the installation again."

(pardon any typos in the error messages since I wasn't able to copy the text directly.)

I attempted this twice with the same result.

Thanks,
Tom