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yocto_css.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

#  yocto-css, an extremely bare minimum CSS parser
#
#  Copyright 2009 Jeff Schiller
#
#  This file is part of Scour, http://www.codedread.com/scour/
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.

# In order to resolve Bug 368716 (https://bugs.launchpad.net/scour/+bug/368716)
# scour needed a bare-minimum CSS parser in order to determine if some elements
# were still referenced by CSS properties.

# I looked at css-py (a CSS parser built in Python), but that library 
# is about 35k of Python and requires ply to be installed.  I just need 
# something very basic to suit scour's needs.

# yocto-css takes a string of CSS and tries to spit out a list of rules
# A rule is an associative array (dictionary) with the following keys:
# - selector: contains the string of the selector (see CSS grammar)
# - properties: contains an associative array of CSS properties for this rule

# TODO: need to build up some unit tests for yocto_css

# stylesheet  : [ CDO | CDC | S | statement ]*;
# statement   : ruleset | at-rule;
# at-rule     : ATKEYWORD S* any* [ block | ';' S* ];
# block       : '{' S* [ any | block | ATKEYWORD S* | ';' S* ]* '}' S*;
# ruleset     : selector? '{' S* declaration? [ ';' S* declaration? ]* '}' S*;
# selector    : any+;
# declaration : property S* ':' S* value;
# property    : IDENT;
# value       : [ any | block | ATKEYWORD S* ]+;
# any         : [ IDENT | NUMBER | PERCENTAGE | DIMENSION | STRING
#               | DELIM | URI | HASH | UNICODE-RANGE | INCLUDES
#               | DASHMATCH | FUNCTION S* any* ')' 
#               | '(' S* any* ')' | '[' S* any* ']' ] S*;

def parseCssString(str):
      rules = []
      # first, split on } to get the rule chunks
      chunks = str.split('}')
      for chunk in chunks:
            # second, split on { to get the selector and the list of properties
            bits = chunk.split('{')
            if len(bits) != 2: continue
            rule = {}
            rule['selector'] = bits[0].strip()
            # third, split on ; to get the property declarations
            bites = bits[1].strip().split(';')
            if len(bites) < 1: continue
            props = {}
            for bite in bites:
                  # fourth, split on : to get the property name and value
                  nibbles = bite.strip().split(':')
                  if len(nibbles) != 2: continue
                  props[nibbles[0].strip()] = nibbles[1].strip()
            rule['properties'] = props
            rules.append(rule)
      return rules

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