python thread group argument must be none for now

http://stackoverflow.com/questions/15349997/assertionerror-when-threading-in-python
出错的代码：
t = threading.Thread(crawl_temp, args=(thread_count, target_url, max_depth, crawl_timeout, crawl_interval))
加上target即可：
t = threading.Thread(target=crawl_temp, args=(thread_count, target_url, max_depth, crawl_timeout, crawl_interval))
就可以了