Issue6877 (and subsequent fixes in Issue8066) allows the Python readline module to be built and linked with the OS X editline (libedit) library rather than with the GNU readline library (which is not included with OS X).  However, the libedit included in versions of OS X prior to 10.5 is considered too broken to use here.

By default, if you do not specify an --with-universal-archs other than "32-bit" to configure or if you do not explicitly set MACOSX_DEPLOYMENT_TARGET to another value, configure defaults to using "10.4" (or earlier) so the building of the readline module is skipped.  You can check this:

>>> from distutils.sysconfig import get_config_var 
>>> get_config_var('MACOSX_DEPLOYMENT_TARGET')
'10.4'

(Whether this is the best default is another question.)

As it stands, to be able to build the readline module, either:

(1) supply the GNU readline library as a local library, or

(2) ensure you are building with a deployment target of at least 10.5.  For example:

    ./configure MACOSX_DEPLOYMENT_TARGET=10.6 ; make

Also note that option (2) is not available for 3.1.x since the changes to support editline/libedit were not ported to it; they are, however, in 2.6.5, 2.7 (trunk), and 3.2 (py3k).