Get top keywords categories

def get_cats(self):
        '''Get top keywords categories'''
        start_url = 'http://top.taobao.com/index.php?from=tbsy'
        rs = self.fetch(start_url)
        if not rs: return None
        soup = BeautifulSoup(rs.content, convertEntities=BeautifulSoup.HTML_ENTITIES, markupMassage=hexentityMassage)
        cats = [{'id':'TR_%s'%li['id'].encode('utf-8').upper(), 'title':li.a.text.encode('utf-8').strip()} for li in soup.find('div', id='nav').findAll('li') if li['id']!='index']
        threadPool = ThreadPool(len(cats) if len(cats)<=5 else 5)
        for cat in cats:
            threadPool.run(self.get_cats_thread, callback=None, cat=cat)
        cats = threadPool.killAllWorkers(None)
        return cats