readlineの環境としてはHomebrewでインストールしたreadline6.2.4。PythonのDependenciesに含まれてるので、普通にbrew install pythonしてれば入ってますeasy_install readlineやpip install ...

Stand-alone readline module Some platforms, such as Mac OS X, do not ship with GNU readline installed. The readline extension module in the standard library of Mac "system" Python uses NetBSD's ...