Comando para instalar Python3.6 en Mac OS
$ brew switch python 3.7.4_1
Blue Bug
$ brew switch python 3.7.4_1
$ brew switch python 3.6.5_1
$ brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb
$ brew unlink python