first you need to download the installer for Python

Welcome to Python.org
The official home of the Python Programming Language
Python.org
  • Windows

you will greeted by this page

first you will go to download

and you will press Download Python (pick the version that you need, and if you willing to do any work that related to deep learning I recommend 3.8 series)

after downloading the installer

make sure to check the "Add Python 3.x to PATH"

  • Mac

First of all, we need to Install Homebrew so go to

Homebrew
The Missing Package Manager for macOS (or Linux).
Homebrew

and you will greeted by this page

copy the line that below "Install Homebrew"

after that type 

 brew install python
  • Linux

Open Terminal and type

sudo apt update
sudo apt install software-properties-common
sudo add-apt-repository spa:deadsnakes/ppa
sudo apt install python 3.8.6