ipython complaining about readline

If you don't mind mucking around with your PYTHONPATH, here's how you can get rid of that pesky warning:

# move site-packages to the front of your sys.path
import sys
for i in range(len(sys.path)):
    if sys.path[i].endswith('site-packages'):
        path = sys.path.pop(i)
        sys.path.insert(0, path)
        break

If you're using Django, you can put this in the ipython method of your site-packages/django/core/management/commands/shell.py so that it runs when you run ./manage.py shell.

When pip installs readline, it will never be imported, because readline.so goes in site-packages, which ends up behind the libedit System one, located in lib-dynload (OSX Python path order is very odd). easy_install -a readline will actually install usable readline.

So you can either use easy_install, or use pip and muck about with your PYTHONPATH/sys.path (which essentially means: DO NOT USE PIP).

A bit more detail on the IPython list (though there really isn't anything IPython-specific about this issue): http://mail.scipy.org/pipermail/ipython-user/2011-September/008426.html

EDIT: extra note about virtualenv.

There is a bug in virtualenv < 1.8.3, where readline would not be properly staged when you create an env.