ANN: Pyrr 0.1 - Lexer and LR(1)-Parser Generator for Python

[Norman Shelley]

FWIW: This has a similiar look/feel to how sabbey wrapped dparser.
http://staff.washington.edu/sabbey/py_dparser/

Heiko Wundram wrote:
> Hi list!
> 
> Not long ago I was looking for an easy to use, but powerful parser and lexer 
> generating tool for Python, and to my dismay, I found quite a number of 
> Python projects implementing an (LA)LR(1) parser generator, but none of them 
> seemed quite finished, or even pythonic.
> 
> As I required a parser generator for Python for one of my work projects, I set 
> out to write (yet another one), and currently am at (release-)version 0.1 for 
> Pyrr.ltk and ptk.
> 
> An example for Pyrr.ltk and ptk usage implementing a (very) simple calculator:
> 
> <<<
> # -*- coding: iso-8859-15 -*-
> 
> from ltk import LexerBase, IgnoreMatch
> from ptk import ParserBase
> from operator import add, sub, mul, div
> 
> class NumLexer(LexerBase):
> 
>     def number(self,value):
>         """number -> r/[0-9]+/"""
>         return float(value)
> 
>     def ws(self,*args):
>         """ws -> r/\\s+/"""
>         raise IgnoreMatch
> 
>     def ops(self,op):
>         """addop -> /+/
>                  -> /-/
>            mulop -> /*/
>                  -> r/\\//"""
>         return op
> 
> class NumParser(ParserBase):
>     """/mulop/: left
>        /addop/: left"""
>     __start__ = "term"
> 
>     def term(self,value1,op,value2):
>         """term -> term /addop/ term
>                 -> term /mulop/ term"""
>         return {"+":add,"-":sub,"*":mul,"/":div}[op](value1,value2)
> 
>     def value(self,value):
>         """term -> /number/"""
>         return value
> 
> print NumParser.parse(NumLexer.tokenize("3 + 4 - 123 / 23"))
> <<<
> 
> Grammar rules and lexemes are specified in docstrings, where lines not 
> matching a definition of a rule or lexeme are ignored. The resulting lexer 
> and parser class is, thus, very much self-documenting, which was one of my 
> biggest goals for the project.
> 
> I'm currently in the process of writing documentation for both packages (and 
> especially documenting the extensions to BNF-grammars that Pyrr.ptk allows, 
> such as your usual RE-operators ?, *, + and {x,y}, and forward arguments, and 
> documenting the stateful lexer support that Pyrr.ltk implements), but I 
> thought that I'd release early and often, so that people interested in this 
> project might have a look at it now to input suggestions and extensions that 
> they'd like me to add to make this a fully featured Python parser generating 
> toolkit which might be offered as a Python package.
> 
> Anyway, the sources can be downloaded (via subversion) from:
> 
> http://svn.modelnine.org/svn/Pyrr/trunk
> 
> where I'll check in the documentation that I've written so far and a Python 
> distutils distribution over the weekend, and make sure that I don't check in 
> brocken code from now on. And, Pyrr.* is Python 2.4 only at the moment, and I 
> have no plans to make it backwards-compatible, but if you're interested in 
> backporting it, feel free to mail me patches.
> 
> --- Heiko.