[译]Tornado并发爬虫

    import time    from datetime import timedelta    try:        from HTMLParser import HTMLParser        from urlparse import urljoin, urldefrag    except ImportError:        from html.parser import HTMLParser        from urllib.parse import urljoin, urldefrag    from tornado import httpclient, gen, ioloop, queues

    base_url = 'http://www.tornadoweb.org/en/stable/'
    concurrency = 10


    @gen.coroutine
    def 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)    def remove_fragment(url):
        pure_url, frag = urldefrag(url)        return pure_url    def get_links(html):
        class URLSeeker(HTMLParser):
            def __init__(self):
                HTMLParser.__init__(self)
                self.urls = []            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.coroutine
    def 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)