我有一个Mac，想要安装python 3.6 我尝试过：
$brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb
但是得到了：
Error: Calling Installation of python from a GitHub commit URL is disabled! Use 'brew extract python' to stable tap on GitHub instead.
所以我尝试了：
$brew extract python https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb
但是得到了：
Error: Invalid tap name 'https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb'
我该怎么办？