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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: PEP/GSoC idea: built-in parser generator module for Python?
Date: Fri, 14 Mar 2014 15:48:23 -0400
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On 3/14/2014 2:51 PM, Peter Mawhorter wrote:
> First of all, hi everyone, I'm new to this list.

Welcome.

> I'm a grad student who's worked on and off with Python on various
> projects for 8ish years now. I recently wanted to construct a parser
> for another programing language in Python and was dissapointed that
> Python doesn't have a built-in module for building parsers, which
> seems like a common-enough task. There are plenty of different
> 3rd-party parsing libraries available, specialized in lots of
> different ways (see e.g., [1]). I happened to pick one that seemed
> suitable for my needs but didn't turn out to support the recursive
> structures that I needed to parse. Rather than pick a different one I
> just built my own parser generator module, and used that to build my
> parser: problem solved.
>
> It would have been much nicer if there were a fully-featured builtin
> parser generator module in Python, however, and the purpose of this
> email is to test the waters a bit: is this something that other people
> in the Python community would be interested in? I imagine the route to
> providing a built-in parser generator module would be to first canvass
> the community to figure out what third-party libraries they use, and
> then contact the developers of some of the top libraries to see if
> they'd be happy integrating as a built-in module. At that point
> someone would need to work to integrate the chosen third-party library
> as a built-in module (ideally with its developers).

I think the idea has been raised before, but I am not sure which list 
(this one, pydev, or python-ideas).

My first reaction, as a core developer, is that the stdlib is, if 
anything, too large. It is already not as well-maintained as we would like.

My second is that parser generation is an application, not a library. A 
parser generator is used by running it with an input specification, not 
by importing it and using specific functions and classes.

>  From what I've looked at PyParsing and PLY seem to be standout parser
> generators for Python, PyParsing has a bit more Pythonic syntax from
> what I've seen. One important issue would be speed though: an
> implementation mostly written in C for low-level parsing tasks would
> probably be much preferrable to one written in pure Python, since a
> builtin module should be geared towards efficiency, but I don't
> actually know exactly how that would work (I've both extended and
> embedded Python with/in C before, but I'm not sure how that kind of
> project relates to writing a built-in module in C).

Something written in Python can be run with any implementation of 
Python. Something written in C tends to be tied to CPython,


> Sorry if this is a bit rambly, but I'm interested in feedback from the
> community on this idea: is a builtin parser generator module
> desirable? If so, would integrating PyParsing as a builtin module be a
> good solution? What 3rd-party parsing module do you think would serve
> best for this purpose?

> [1] http://nedbatchelder.com/text/python-parsers.html

Perhaps something like this should be in the wiki, if not already.

-- 
Terry Jan Reedy