how to install python3 in ubuntu

# first do:
sudo apt-get update
# after do:
sudo apt-get install python3.6
# then it should be installed

sudo apt-get install python3.7

sudo apt update
sudo apt install software-properties-common
sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update
sudo apt install python3.8

sudo apt install software-properties-common