> It would also be nice if one could programmaticly detect if readline
> is linked to libedit

There's this rl_library_version constant defined in editline/readline C 
libraries that the attached patch uses.
Perhaps, if we can expose its value from the Python readline module, one 
could check whether the value startswith("EditLine wrapper") in ipython 
and similar programs.

Regarding your comment about editline being broken on Leopard:  The 
patch worked just fine for me and other people who used it in my 
company.  We used line editing and history in interactive interpreter 
with both Python 2.4 and Python 2.6 on Leopard.

One person used it with Python 2.4 and ipython.  He did not have a 
readline functionality until he compiled with the patch.  After applying 
the patch the line editing, history and TAB completion worked for him in 
ipython.  He's now running Snow Leopard so we couldn't check one more 
time.
 
Perhaps you meant it was broken on Tiger (10.4; Darwin 8).