When installing python3.6 on ubuntu16.04 etc. ppa:jonathonf/python-3.6 I was using the ppa of, but I was a little troubled because it became private, so a memo
sudo add-apt-repository ppa:jonathonf/python-3.6 sudo apt update sudo apt install python3.6
Log at the time of apt update
W: The repository 'http://ppa.launchpad.net/jonathonf/python-3.6/ubuntu xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. E: Failed to fetch http://ppa.launchpad.net/jonathonf/python-3.6/ubuntu/dists/xenial/main/binary-amd64/Packages 403 Forbidden [IP: 22.214.171.124 80] E: Some index files failed to download. They have been ignored, or old ones used instead.
Changed ppa to ppa:deadsnakes/ppa
sudo add-apt-repository ppa:deadsnakes/ppa sudo apt update sudo apt install python3.6
You can put it here