[Python-Dev] info/advices about python readline implementation

[Gregory Lielens]

Hi,

Lisandro Dalcin and me are working on a common version of our patches
([1232343],[955928]) that we plan to submit soon (this would close the
two previously proposed patches, and we plan also to review 5 other
patches to push this one before 2.5 ;-) ). 

We would like this new patch to be as clean and as safe as possible, but
to do so we would need some infos/advices from the list, and in
particular peoples having worked in the readline C implementation, i.e.
in modules Modules/readline.c,  Parser/myreadline.c (PyOS_StdioReadline,
PyOS_StdioReadline, vms__StdioReadline), Python/bltinmodule.c
(builtin_raw_input).

First a general question about implementation guidelines for CPython:
   -is it ok to initialize a static pointer to a non-null value (the
address of a predefined function) at compile time? ANSI-C (or even
pre-ansi C afaik) accept this, we have tested it on various linux and
unix, and there are occurrences of similar construct in the python C
sources, but not so many and not for function pointers (or I did not
found it ;) ).
We wonder if this can cause problem on some platforms not correctly
implementing C standard(s) but that python have to support nonetheless,
or if there is a feeling against it...The idea is to initialize
PyOS_ReadlineFunctionPointer this way.

Then something about the VMS platform support:
  -readline seems to make uses of the extern function
vms__StdioReadline() on VMS...Where can we find the source or doc about
this function? In particular, we would like to know if this function
call (or can call) PyOS_StdioReadline, which would cause infinite
recursion in some version of our patchwithout havind access to VMS
for testing or info about vms__StdioReadline, this is impossible to
know...

Thanks for any info,

Greg.

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Re: [Python-Dev] info/advices about python readline implementation

[Gregory Lielens]

> > Then something about the VMS platform support:
> >   -readline seems to make uses of the extern function
> > vms__StdioReadline() on VMS...Where can we find the source or doc about
> > this function? In particular, we would like to know if this function
> > call (or can call) PyOS_StdioReadline, which would cause infinite
> > recursion in some version of our patchwithout havind access to VMS
> > for testing or info about vms__StdioReadline, this is impossible to
> > know...
> 
> I have no idea; Googling for it only showed up discussions of
> readline.c. You might write the authors of the patch that introduced
> it (the same Google query will find the info); if they don't respond,
> I'm not sure that it's worth worrying about.

Googling only returned comments or queries by either Lisandro or me, but
it was loewis (Martin v. Löwis ?) that comited this change in May 2003
with the comment Patch #708495: Port more stuff to OpenVMS.

Tha patch was introduced by Jean-François Piéronne, who explained: 

myreadline.c
Use of vms__StdioReadline

> My personal guess is that it's probably a VMS internal function, which
> would reduce the probability of it calling back to PyOS_StdioReadline
> to zero. It can't be a Python specific thing, because it doesn't have
> a 'Py' prefix.

My guess too, especially as using PyOS_StdioReadline (which is not in
the python API) would be asking for trouble...We will thus consider that
there is no risk of infinite recursion, except if someone say
otherwise...

Thanks a lot for these fast and usefull informations!


Greg.

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