Python tornado队列示例-一个并发web爬虫代码分享

import timefrom datetime import timedeltatry: from HTMLParser import HTMLParser from urlparse import urljoin, urldefragexcept ImportError: from html.parser import HTMLParser from urllib.parse import urljoin, urldefragfrom tornado import httpclient, gen, ioloop, queuesbase_url = 'http://www.tornadoweb.org/en/stable/'concurrency = 10@gen.coroutinedef get_links_from_url(url): """Download the page at `url` and parse it for links. Returned links have had the fragment after `#` removed, and have been made absolute so, e.g. the URL 'gen.html#tornado.gen.coroutine' becomes 'http://www.tornadoweb.org/en/stable/gen.html'. """ try:  response = yield httpclient.AsyncHTTPClient().fetch(url)  print('fetched %s' % url)  html = response.body if isinstance(response.body, str) /   else response.body.decode()  urls = [urljoin(url, remove_fragment(new_url))    for new_url in get_links(html)] except Exception as e:  print('Exception: %s %s' % (e, url))  raise gen.Return([]) raise gen.Return(urls)#用于从一个包含片段的url中提取中真正的url.def remove_fragment(url):   pure_url, frag = urldefrag(url) return pure_urldef get_links(html): class URLSeeker(HTMLParser):  def __init__(self):   HTMLParser.__init__(self)   self.urls = []	#从所有a标签中提取中href属性。  def handle_starttag(self, tag, attrs):   href = dict(attrs).get('href')   if href and tag == 'a':    self.urls.append(href) url_seeker = URLSeeker() url_seeker.feed(html) return url_seeker.urls@gen.coroutinedef main(): q = queues.Queue() start = time.time() fetching, fetched = set(), set() @gen.coroutine def fetch_url():  current_url = yield q.get()  try:   if current_url in fetching:    return   print('fetching %s' % current_url)   fetching.add(current_url)   urls = yield get_links_from_url(current_url)   fetched.add(current_url)   for new_url in urls:    # Only follow links beneath the base URL    if new_url.startswith(base_url):     yield q.put(new_url)  finally:   q.task_done() @gen.coroutine def worker():  while True:   yield fetch_url() q.put(base_url) # Start workers, then wait for the work queue to be empty. for _ in range(concurrency):  worker() yield q.join(timeout=timedelta(seconds=300)) assert fetching == fetched print('Done in %d seconds, fetched %s URLs.' % (  time.time() - start, len(fetched)))if __name__ == '__main__': import logging logging.basicConfig() io_loop = ioloop.IOLoop.current() io_loop.run_sync(main)