This is MapCSS parser I use in my OSM rendering. I've tried to implement spec 
from http://wiki.openstreetmap.org/wiki/MapCSS but it's not very formal, so 
the implementation may doesn't match with your vision of MapCSS. 
This parser use PLY (http://www.dabeaz.com/ply) library. 

== Dependency
sudo pip install ply

== Installation
sudo python setup.py install

== Layout
mapcss_parser/ast.py             - Abstract Syntax Tree classes
mapcss_parser/lex.py             - Lexer
mapcss_parser.py                 - MapCSS parser entry point
mapcss_parser/parse.py           - Parser
test/parser_test.py     - Unit tests of MapCSS parser

== Usage
Simple way to see MapCSS parser in action is use CLI:

> python mapcss-parser.py <YOUR_MAP_CSS_FILE>

This script will parse your file to AST, and build it again from AST to MapCSS. Not very useful, ah?

More complex example. I use this parser to convert MapCSS to the code. So I've just mixed-in 
necessary methods directly to AST classes. 

import sys
sys.path.insert(0,"../mapcss-parser")

from mapcss_parser import MapCSSParser

import ast

if len(sys.argv) != 2:
    print "usage : mapcss.py inputfile"
    raise SystemExit

content = open(sys.argv[1]).read()
parser = MapCSSParser(debug=False)
mapcss = parser.parse(content)

def mapcss_convert(self):
    imports = "".join(map(lambda imp: propagate_import(imp.url).as_js, self.imports))
    rules = "\n".join(map(lambda x: x.as_js(), self.rules))
    return "%s%s" % (imports, rules)

ast.MapCSS.convert = mapcss_convert

... And so on for other 13 AST classes

print mapcss.convert()

If you have questions about MapCSS parser, you can find me on #osm and #osm_ru IRC channels, of e-mail me to <mr.miroff@gmail.com>