pyenv

readme.md

# make sure to have these libs to compile Python with
sudo apt install -y libssl-dev openssl zlib1g-dev sqlite3 libsqlite3-dev libbz2-dev bzip2

# download pyenv
git clone https://github.com/pyenv/pyenv.git ~/.pyenv

# put it in your path and initialize it, in .bashrc for example
export PATH="${HOME}/.pyenv/bin:${PATH}"
eval "$(pyenv init -)"

# now install all the versions you need (it can indeed take some time)
pyenv install 3.5.3
pyenv install 3.6.1
pyenv install 3.7-dev

# and last but very important step, run this once:
pyenv global system 3.5.3 3.6.1 3.7-dev
# the order is important, list all the installed versions you want to use
# thanks to that, tox will find all the executables
# "system" should always be first so we keep normal behavior when not in a virtualenv

http://tox.readthedocs.io/en/latest/