[Python-Dev] PLY in stdlib (was cffi in stdlib)

David Beazley dave at dabeaz.com
Wed Feb 27 12:00:17 CET 2013

> From: Eli Bendersky <eliben at gmail.com>
> I'll be the first one to admit that pycparser is almost certainly not
> generally useful enough to be exposed in the stdlib. So just using it as an
> implementation detail is absolutely fine. PLY is a more interesting
> question, however, since PLY is somewhat more generally useful. That said,
> I see all this as implementation details that shouldn't distract us from
> the main point of whether cffi should be added.

Regarding the inclusion of PLY or some subcomponent of it in the standard library, it's not an entirely crazy idea in my opinion.  LALR(1) parsers have been around for a long time, are generally known to anyone who's used yacc/bison, and would be useful outside the context of cffi or pycparser.  PLY has also been around for about 12 years and is what I would call stable.  It gets an update about every year or two, but that's about it.   PLY is also relatively small--just two files and about 4300 lines of code (much of which could probably be scaled down a bit).

The only downside to including PLY might be the fact that there are very few people walking around who've actually had to *implement* an LALR(1) parser generator.  Some of the code for that is extremely hairy and mathematical.   At this time, I don't think there are any bugs in it, but it's not the sort of thing that one wants to wander into casually.    Also, there are some horrible hacks in PLY that I'd really like to get rid of, but am currently stuck with due to backwards compatibility issues. 

Alex Gaynor has been working on a PLY variant (RPLY) geared at RPython and which has a slightly different programming interface.    I'd say if we were to go down this route, he and I should work together to put together some kind of more general "parsing.lalr" package (or similar) that  cleans it up and makes it more suitable as a library for building different kinds of parsing tools on top of. 


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