[Python-Dev] readline.clear_history()

[Phillip J. Eby]

At 02:45 PM 8/27/03 -0700, Guido van Rossum wrote:
> > I've been working on a set of Python tools that use readline, but want to
> > keep history separate between different interaction modes.  Unfortunately,
> > this really needs to be able to access readline's clear_history(), as
> > read_history_file() leaves existing history intact.
>
>Sounds like a good feature.
>
> > I'd be happy to whip up a patch to add this (as readline.clear_history()),
> > but I was wondering if perhaps the reason it's not currently exported by
> > the readline module is a compatibility issue for older readline
> > implementations that are officially supported.  Thanks.
>
>It's probably laziness.  When I created the initial readline module, I
>didn't know anything about the C API of GNU readline.  All I wanted
>was basic readline functionality, and I applied the YAGNI principle
>vigorously.  Gradually, various people have added APIs for various
>useful GNU readline APIs.
>
>But there might be a version issue as well.  I have various versions
>of the readline sources online just for this purpose (GNU readline is
>notorious for not providing an easy way to check at compile-time which
>version you are using), and I note that clear_history() is present in
>2.2, but not in 2.0.  I seem to recall that 2.2 is the oldest widely
>used version, so I think you're safe.

Hmmm...  the CVS log for Modules/readline.c makes mention of changes made 
to assure backward compatibility with readline 2.1 and 2.0, and #ifdefs 
some items as a result.  I suppose I could wrap a clear_history in the 
same.  However, that leads to a couple of questions:

* Should clear_history() only appear in the readline module if the facility 
exists?

* If it should always appear, should it be a no-op if the facility isn't 
available, or raise an error?

"Errors should never pass silently" suggests that if it does appear, it 
should raise an error if the facility doesn't exist.  So, I guess the 
question is, should you get an error trying to access clear_history(), or 
an error calling it?  (And in the latter case, is NotImplementedError the 
right thing to raise?)

Last question (I hope): as a feature, I presume this has to wait for 2.4 to 
get in, yes?