A quick and dirty CSS parser using Parsimonious

parse_css.py

from parsimonious import Grammar
from parsimonious.nodes import NodeVisitor


# Adapted from https://raw.github.com/bhyde/css-parser/master/css.peg:
# This is an incredibly inefficient grammar, but it would be simple to
# optimize. Eventually, Parsimonious will know how to do that automatically.
css = Grammar(r"""
    program = S* stylesheet
    digit = ~"[0123456789]"
    nmstart = ~"[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_]"
    nmchar = nmstart / ~"[0123456789-]"
    minus = "-"
    IDENT = nmstart nmchar*
    NUMBER = digit+ / (digit* "." digit+)
    ws = ~r"[ \t]"
    nl = ~r"[\n]"
    comment = "/*" (!"*/" ~".")* "*/"
    ws_or_nl = ws / nl
    S = ws_or_nl / comment
    stylesheet = stmt*
    stmt = rule / media
    rule = rule_lhs rule_rhs
    rule_lhs = selector more_selector*
    more_selector =  "," S* selector
    rule_rhs = "{" decls  ";"? S* "}" S*
    decls = S* declaration more_declaration*
    more_declaration = ";" S* declaration

    selector = simple_selector selector_trailer?
    selector_trailer = selector_trailer_a / selector_trailer_b / selector_trailer_c / selector_trailer_d
    selector_trailer_a = combinator selector
    selector_trailer_b = S+ combinator selector
    selector_trailer_c = S+ selector
    selector_trailer_d = S+

    simple_selector = (element_name simple_selector_etc*) / (simple_selector_etc+)
    simple_selector_etc = id_selector / class_selector / attrib_selector / pseudo_selector

    element_name = element_selector / wild_element_selector
    element_selector = IDENT
    wild_element_selector = "*"

    id_selector     = "#" IDENT
    class_selector  = "." IDENT
    attrib_selector = "[" S* IDENT ( ("=" / "~=" / "|=" ) S* ( IDENT / STRING ) S*)? "]"
    pseudo_selector = ":" IDENT
    tbd_pseudo_selector = ":" IDENT ( "(" ( IDENT S* )? ")" )?

    combinator = ("+" / ">") S*

    declaration = property ":" S* expr prio?
    property = IDENT S*
    prio = "!" S*
    expr = term ( operator? term )*
    operator = operator_a S*
    operator_a =  "/" / ","
    term = (unary_op measure) / measure / other_term
    unary_op = "-" / "+"
    measure = mess S*
    mess = em_m / ex_m / px_m / cm_m / mm_m / in_m / pt_m / pc_m / deg_m / rad_m / grad_m / ms_m / s_m / hx_m / khz_m / precent_m / dim_m / raw_m
    em_m = NUMBER "em"
    ex_m = NUMBER "ex"
    px_m = NUMBER "px"
    cm_m = NUMBER "cm"
    mm_m = NUMBER "mm"
    in_m = NUMBER "in"
    pt_m = NUMBER "pt"
    pc_m = NUMBER "pc"
    deg_m = NUMBER "deg"
    rad_m = NUMBER "rad"
    grad_m = NUMBER "grad"
    ms_m = NUMBER "ms"
    s_m = NUMBER "s"
    hx_m = NUMBER "hz"
    khz_m = NUMBER "khz"
    precent_m = NUMBER "%"
    dim_m = NUMBER IDENT
    raw_m = NUMBER

    other_term = (STRING S*) / (URI S*) / (IDENT S*) / (hexcolor S*) / function

    function = IDENT "(" S* expr ")" S*
    STRING = '"' ( !'"' ~"." )* '"'
    URI = "url(" ( !")" ~"." )* ")"
    hexcolor = ("#" hex hex hex hex hex hex) / ("#" hex hex hex)
    hex = ~r"[0123456789abcdefABCDEF]"


    medium = IDENT S*
    medium_list = medium ("," S* medium)*
    media = "@media" S* medium "{" S* stylesheet "}"
    """)


# class CssVisitor(NodeVisitor):
#     def visit_selector(self, selector, (simple_selector, optional_trailer)):
#         print "A selector: %s" % simple_selector
# 
#     def generic_visit(self, node, visited_children):
#         return node
# 
# 
tree = css.parse("""
    p {
        thing: 4em;
    }
    """)
print tree
# 
# print CssVisitor().visit(tree)

# The next step would be to figure out how you want to transform the AST and
# write a NodeVisitor subclass (or something custom) to do it.