Installing Python 3 on Mac OS X
The latest version of Mac OS X, Sierra, comes with Python 2.7 out of the box.
Python 2.7.10 (default, Jul 30 2016, 19:40:32)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
You do not need to install or configure anything else to use Python 2. These instructions document the installation of Python 3.
The version of Python that ships with OS X is great for learning but it’s not good for development. The version shipped with OS X may be out of date from the official current Python release, which is considered the stable production version.