Resolving Readline Errors When Running iPython

When I switched to MacOS Lion and was setting up my environment, I encountered the following error when running iPython:

(省略)/python2.7/site-packages/IPython/utils/rlineimpl.py:96: RuntimeWarning: Leopard libedit detected - readline will not be well behaved including some crashes on tab completion, and incorrect history navigation. It is highly recommended that you install readline, which is easy_installable with: 'easy_install readline'
  RuntimeWarning

This error disappeared after running the command:

$ easy_install-2.7 -a readline