Installing Python 3 on Mac OS
As of 2016, Macs come with Python 2.7.x installed.
The python installer for Mac OS is a installer package as opposed to something that can be installed on the command line.
Search for "Install Python 3" to find the Python download page.
Download the 64-bit Python installer package for Mac OS.
(The installer doesn't require admin privileges.)
See Python Virtual Environments for running Python 3.