Installs Python 3.6.8 on an Ubuntu distribution (https://www.quora.com/How-can-one-install-a-specific-version-of-Python-in-Ubuntu)

python36.sh

sudo apt-get install build-essential checkinstall
sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev libffi-dev

cd ~/Downloads/
wget https://www.python.org/ftp/python/3.6.8/Python-3.6.8.tgz

tar -xvf Python-3.6.8.tgz
cd Python-3.6.8
./configure
make
sudo checkinstall
# When asked about files in the /home directory and in the /home/<username>/Downloads/Python-3.6.8 directories, opt to remove them. Copying the temporary files will take a long time