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Resources for lexing, tokenising and parsing in python

Asked 2008-08-31T16:50:35.453
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Can people point me to resources on lexing, parsing and tokenising with Python?

I'm doing a little hacking on an open source project (hotwire) and wanted to do a few changes to the code that lexes, parses and tokenises the commands entered into it. As it is real working code it is fairly complex and a bit hard to work out.

I haven't worked on code to lex/parse/tokenise before, so I was thinking one approach would be to work through a tutorial or two on this aspect. I would hope to learn enough to navigate around the code I actually want to alter. Is there anything suitable out there? (Ideally it could be done in an afternoon without having to buy and read the dragon book first ...)

Edit: (7 Oct 2008) None of the below answers quite give what I want. With them I could generate parsers from scratch, but I want to learn how to write my own basic parser from scratch, not using lex and yacc or similar tools. Having done that I can then understand the existing code better.

So could someone point me to a tutorial where I can build a basic parser from scratch, using just python?

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2 Answers

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Here's a few things to get you started (roughly from simplest-to-most-complex, least-to-most-powerful):

http://en.wikipedia.org/wiki/Recursive_descent_parser

http://en.wikipedia.org/wiki/Top-down_parsing

http://en.wikipedia.org/wiki/LL_parser

http://effbot.org/zone/simple-top-down-parsing.htm

http://en.wikipedia.org/wiki/Bottom-up_parsing

http://en.wikipedia.org/wiki/LR_parser

http://en.wikipedia.org/wiki/GLR_parser

When I learned this stuff, it was in a semester-long 400-level university course. We did a number of assignments where we did parsing by hand; if you want to really understand what's going on under the hood, I'd recommend the same approach.

This isn't the book I used, but it's pretty good: Principles of Compiler Design.

answered 2008-11-11T01:13:42.507
3

I suggest http://www.canonware.com/Parsing/, since it is pure python and you don't need to learn a grammar, but it isn't widely used, and has comparatively little documentation. The heavyweight is ANTLR and PyParsing. ANTLR can generate java and C++ parsers too, and AST walkers but you will have to learn what amounts to a new language.

answered 2008-08-31T23:14:54.283

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