Plyplus is a general-purpose parser built on top of PLY (http://www.dabeaz.com/ply/), written in python, with a slightly different approach to parsing.

Most parsers work by calling a function for each rule they identify, which processes the data and returns to the parser. Plyplus parses the entire file into a parse-tree, letting you search and process it using visitors and pattern-matching.

Plyplus makes two uncommon separations: of code from grammar, and of processing from parsing. The result of this approach is (hopefully) a cleaner design, more powerful grammar processing, and a parser which is easier to write and to understand.

Features:

Automatically builds an AST. Customizable in grammar (expand and flatten nodes automatically)
Selectors: run powerful queries on the AST
Rule operators mimicking regular expressions (supported: parentheses, '|', '*', '?', and '+')
Comes with a full, flexible, Python grammar
Nested grammars (a grammar within a grammar. Useful for HTML/CSS, for example)
Automatic line counting
From PLY: Readable errors, Debug mode
And more! ...