in Formula/aws-sam-cli-rc.rb [23:30]
def install
venv = virtualenv_create(libexec, "python3.7")
system libexec/"bin/pip", "install", "pip==19.2.3"
system libexec/"bin/pip", "install", "-v", "--pre", "--ignore-installed", buildpath
system libexec/"bin/pip", "uninstall", "-y", "aws-sam-cli"
venv.pip_install_and_link buildpath
end