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This is a request to expose the `callback API`_ of GNU readline in the readline module in the Python library.
.. _callback API: http://cnswww.cns.cwru.edu/php/chet/readline/readline.html#SEC41
This interface is suitable for asynchronous use, such as with twisted.
It is possible to expose the functions on Unix with ctypes::
 import readline
 import ctypes
 rl_lib = ctypes.cdll.LoadLibrary("libreadline.so.5")
 readline.callback_handler_remove = rl_lib.rl_callback_handler_remove
 readline.callback_read_char = rl_lib.rl_callback_read_char
 # the callback needs special treatment:
 rlcallbackfunctype = ctypes.CFUNCTYPE(ctypes.c_void_p, ctypes.c_char_p)
 def setcallbackfunc(prompt, thefunc):
 rl_lib.rl_callback_handler_install(prompt, rlcallbackfunctype(thefunc))
 readline.callback_handler_install = setcallbackfunc
but it would be much better to expose them "officially".

A patch is always welcome

I am pretty sure I posted a patch in the sf patch tracker... oh yes,
here it is: http://bugs.python.org/issue1744456
I think it still needs some work if you want to make it impossible for
users of the API to wreck the interactive prompt. If this possibility is
considered ok (it does not make sense to use the callback api from the
interactive prompt anyway), I think it's ok.
But someone with more readline experience should probably look at it... :-)

Can this be closed as a duplicate as Issue1744456 has a patch?

Yes, that makes sense (the two issues come from the SourceForge era, where bugs and patches had different trackers).