Announce : PLY-3.0

David Beazley dave at
Sat Feb 7 13:37:20 CET 2009

February 6, 2009

                  Announcing :  PLY-3.0 (Python Lex-Yacc)


I'm pleased to announce a significant new update to PLY---a 100% Python
implementation of the common parsing tools lex and yacc.  PLY-3.0 adds
compatibility for Python 2.6 and 3.0, provides some new customization
options, and cleans up a lot of internal implementation details.

If you are new to PLY, here are a few highlights:

-  PLY is closely modeled after traditional lex/yacc.  If you know how 
   to use these or similar tools in other languages, you will find
   PLY to be comparable.

-  PLY provides very extensive error reporting and diagnostic
   information to assist in parser construction.  The original
   implementation was developed for instructional purposes.  As
   a result, the system tries to identify the most common types
   of errors made by novice users.

-  PLY provides full support for empty productions, error recovery,
   precedence rules, and ambiguous grammars.

-  Parsing is based on LR-parsing which is fast, memory efficient,
   better suited to large grammars, and which has a number of nice
   properties when dealing with syntax errors and other parsing 
   problems. Currently, PLY can build its parsing tables using 
   either SLR or LALR(1) algorithms. 

More information about PLY can be obtained on the PLY webpage at:


PLY is freely available and is licensed under the terms of the Lesser
GNU Public License (LGPL).


David Beazley (

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