Process Stylus (.styl) files

def stylus(input, output, **kw):
    """Process Stylus (.styl) files"""
    stdin = open(input, 'r')
    stdout = open(output, 'w')
    cmd = '%s --include %s' % (current_app.config.get('STYLUS_BIN'),
                               os.path.abspath(os.path.dirname(input)))
    subprocess.call(cmd, shell=True, stdin=stdin, stdout=stdout)