tldr; install brew; brew install python
Homebrew is a great installer for Mac and its main job is to make it easier to install packages.
Step 1: Download Homebrew here
"brew" hosts its package information here as “formulae“.
Step 2: Use brew to install the latest version of Python
$ brew install python --verbose
Now you can run python3 in your terminal
> python3
More details: So what happens when I run brew install?
When you run the command, brew will look for the package in the “formulae” list and run the installation script for the package.
Brew installs *all* packages into its own directory on your computer at /usr/local/Cellar .
Take a look with $ ls /usr/local/Cellar.
After installation, brew creates a symlink which is basically a shortcut that will allow your system to run the new command > python3.