For windows - Download latest version from the official website:
https://www.python.org/downloads/
For Centos - use yum:
sudo yum install python3
For Ubuntu - use apt-get:
sudo apt install python3
$ sudo add-apt-repository ppa:jonathonf/python-3.6
$ sudo apt-get update
$ sudo apt-get install python3.6
# go to python.org website and download the lastest version
# open the downloaded file and finish all the installing tasks
# go to start type python idle to open a python shell