PyBison is a Python binding to the Bison (yacc) and Flex (lex)
parser-generator utilities.

It allows parsers to be quickly and easily developed as Python class
declarations, and for these parsers to take advantage of the fast and
powerful C-based Bison/Flex.

Users write a subclass of a basic Parser object, containing a set of methods
and attributes specifying the grammar and lexical analysis rules, and taking
callbacks for providing parser input, and receiving parser target events.

Features
     * Runs at near the speed of C-based parsers, due to direct hooks into
       bison-generated C code
     * Full LALR(1) grammar support
     * Includes a utility to convert your legacy grammar (.y) and scanner (.l)
       scripts into python modules compatible with PyBison
     * Easy to understand - the walkthrough and the examples will have you
       writing your own parsers in minutes
     * Comfortable and intuitive callback mechanisms
     * Can export parse tree to XML with a simple method call
     * Can reconstitute a parse tree from XML

WWW: http://www.freenet.org.nz/python/pybison/