Hi,

Leopard ships with libedit, which is almost the same as readline, but 
has another way to configure completion keys. To enable tab completion 
you have to use rl.parse_and_bind("bind ^I complete") instead of rl.parse_and_bind("bind ^I rl_complete") instead of rl.parse_and_bind("tab: complete").

The guys from IPython patched around it, see http://ipython.scipy.org/moin/InstallationOSXLeopard/LeopardPythonReadli
ne, but is seems to me this is better solved in the python readline 
module itself.