get list of allowed parameters

def get_standard(self):
        """get list of allowed parameters"""
        try:
            res = urlopen(PARSELY_PAGE_SCHEMA)
        except:
            return []
        text = res.read()
        if isinstance(text, bytes):
            text = text.decode('utf-8')
        tree = etree.parse(StringIO(text))
        stdref = tree.xpath("//div/@about")
        return [a.split(':')[1] for a in stdref]