[Patches] [ python-Patches-1690201 ] Added support for custom readline functions

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Patches item #1690201, was opened at 2007-03-28 17:52
Message generated for change (Comment added) made by jimjjewett
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Category: Core (C code)
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Ben Timby (btimby)
Assigned to: Nobody/Anonymous (nobody)
Summary: Added support for custom readline functions

Initial Comment:
This patch allows for binding a key or keyseq to a custom function named custom. A custom handler can be registered and will be called by readline when the registered sequence input.

Example:

rl.py
--
import readline

def handler():
    print "need some help?"

readline.set_custom_hook(handler)
readline.parse_and_bind("\"?\": custom")

text = raw_input("type ? for help# ")
--

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Comment By: Jim Jewett (jimjjewett)
Date: 2007-04-24 18:56

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It looks as though you may have code from python 2.3.4 -- readline.c has
been updated somewhat since then, particularly around threading.

I'm not sure I fully understand what you're asking in step 3.  It looks
like on_hook(obj) will already call the python function well enough; you
just need a way of keeping a reference to (and registering) a list of
functions.

The module uses (single) static variables for the hooks it predefines, and
you followed that model; you could just add a list of objects.  Instead of



Then in set_custom_hook, instead of calling set_hook immediately, 

    /* Not tested, you might want a dict instead, you should error check,

       you should pre-declare for C89, etc */

    if (NULL == custom_hooks) custom_hooks=PyList_New(0); /* no initial
elements */

    PyList_Append(custom_hooks, args);  /* add your custom func, etc to
the list */
    set_hook("  ", &(PyList_GET_ITEM(custom_hooks,
PyList_GET_SIZE(custom_hooks))), *args);


(Or you could just inline the checks from set_hook.)

If you're feeling ambitious, you could fix set_hook itself to use a
dictionary instead of specific pointers, or to get the name from the
function.__name__, or to use a newer calling convention (As I understand
it, the registration may really be METH_ONE, instead of METH_VARARGS.)


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Comment By: Ben Timby (btimby)
Date: 2007-04-03 07:59

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Paul, thank you for clarifying. I agree with you completely. The reason I
was unable to implement the API fully is the following problem (probably as
you said due to the lack of dynamic features in C).

1. User defines python function.
2. User calls python readline.add_defun()
3. readline.add_defun() must whip up a C handler that will call the python
function and in turn call rl_add_defun to register it. Problem being that
multiple custom python functions registered with readline to a single C
handler will have no way to determine which python function to call on
invocation.
4. User calls readline.parse_and_bind()

I have no clue how to do step 3, so I avoided it. If anyone has
suggestions, ideas or examples, I am happy to do the work, I simply have
not had to do something like this before in C. I don't even know what this
would be called in order to google for it.

The patch is certainly not as useful as the full API, however, I DID
implement it to solve a problem, thus there is some use to it :-). I
learned recently that I can maintain this feature as an extension (outside
of) python, thus allowing me to continue to use it without depending on
python maintainers to perceive usefulness. I will do this for the time
being and if I am able to figure out item 3 I will resubmit the patch with
a full implementation.

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Comment By: Paul Hankin (paulhankin)
Date: 2007-04-02 13:28

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Hi Ben, I'm sorry if you thought my short reply suggested I hadn't looked
at the patch properly. I'll try to clarify what I meant.

Gnu readline provides an interface to custom functions: you declare a
function that takes a 'count' and a 'key' and returns 0 or an error. You
then call rl_add_defunc to declare it. You use the name you used in
'rl_add_defunc' in the readline init file to bind the command to a key.

The patch uses a different interface: the user provides a function that
takes no arguments. He declares it by calling 'set_custom_hook', and calls
it by using the name 'custom' in the init file to bind it to a key.

An interface consistent between python and readline would be:

def say_hello(key, count):
   ...
readline.add_defunc("say_hello", say_hello)
readline.parse_and_bind('"?" : say_hello')

(Perhaps the 'add_defun' is an artefact of lack of dynamic features of C
and would be dropped from the python interface).

The patch's use of a 'custom' hook is more complicated than using the
function name directly in the init file, and provides less functionality (a
single command, and removes the arguments that the c command would have).
Accepting this patch will cause minor compatibility trouble in future if
anyone works out a way round the admittedly difficult technical problems of
doing things the 'right' way.

Given the interface troubles, I'm not convinced enough of the usefulness
of the patch.


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Comment By: Ben Timby (btimby)
Date: 2007-04-01 21:53

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If by adopt you mean adapt, that is what I have done. I simplified things
to allow a single named function "custom" but it uses the gnu readline
custom function interface (rl_add_defunc) . Have you even looked at the
patch?

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Comment By: Paul Hankin (paulhankin)
Date: 2007-04-01 17:47

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Gnu readline supports custom functions in C - it would be better to adopt
the gnu readline custom function interface to python, rather than using the
'custom' handler which smells of a hack.


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Comment By: Ben Timby (btimby)
Date: 2007-03-28 19:01

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new Example:

rl.py
--
#!/usr/bin/python
import readline

def say_hello():
	print
	print "this is my help text..."
	readline.on_new_line()

readline.set_custom_hook(say_hello)
readline.parse_and_bind("\"?\": custom")

while True:
	data = raw_input("input# ")
	print "data: ", data
--

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Comment By: Ben Timby (btimby)
Date: 2007-03-28 19:00

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File Added: python-2.3.4-readline_custom.patch

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