CODE EXAMPLE FOR SHELL

python-minimal has no installation candidate

 mv /etc/apt/sources.list /etc/apt/sources.list_stor
 apt-get update
 apt-get install python
 Add this root user : 
vi /etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu bionic-updates main restricted universe multiverse 
 Add this root user : 
vi /etc/apt/sources.list
deb http://mirror.kakao.com/ubuntu focal-security main restricted
deb http://mirror.kakao.com/ubuntu focal-security universe
deb http://mirror.kakao.com/ubuntu focal-security multiverse