本文實(shí)例為大家分享了python使用tornado實(shí)現(xiàn)簡單爬蟲的具體代碼，供大家參考，具體內(nèi)容如下

代碼在官方文檔的示例代碼中有,但是作為一個(gè)tornado新手來說閱讀起來還是有點(diǎn)困難的,于是我在代碼中添加了注釋,方便理解,代碼如下:

# coding=utf-8 #!/usr/bin/env pythonimport 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, queues # 設(shè)置要爬取的網(wǎng)址base_url = 'http://www.baidu.com' # 設(shè)置worker數(shù)量concurrency = 10 # 此代碼會(huì)獲取base_url下的所有其他url@gen.coroutinedef get_links_from_url(url):  try:    # 通過異步向url發(fā)起請求    response = yield httpclient.AsyncHTTPClient().fetch(url)    print('fetched %s' % url)    # 響應(yīng)如果是字節(jié)類型 進(jìn)行解碼    html = response.body if isinstance(response.body, str) /      else response.body.decode(errors='ignore')    # 構(gòu)建url列表    urls = [urljoin(url, remove_fragment(new_url))        for new_url in get_links(html)]  except Exception as e:    print('Exception: %s %s' % (e, url))    # 報(bào)錯(cuò)返回空列表    raise gen.Return([])  # 返回url列表  raise gen.Return(urls)def remove_fragment(url):  #去除錨點(diǎn)  pure_url, frag = urldefrag(url)  return pure_urldef get_links(html):  #從html頁面里提取url  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.coroutinedef main():  # 創(chuàng)建隊(duì)列  q = queues.Queue()  # 記錄開始時(shí)間戳  start = time.time()  # 構(gòu)建兩個(gè)集合  fetching, fetched = set(), set()  @gen.coroutine  def fetch_url():    # 從隊(duì)列中取出數(shù)據(jù)    current_url = yield q.get()    try:      # 如果取出的數(shù)據(jù)在隊(duì)列中已經(jīng)存在 返回      if current_url in fetching:        return      print('fetching %s' % current_url)      # 如果不存在添加到集合當(dāng)中      fetching.add(current_url)      # 從新放入的鏈接中繼續(xù)獲取鏈接      urls = yield get_links_from_url(current_url)      # 將已經(jīng)請求玩的url放入第二個(gè)集合      fetched.add(current_url)      for new_url in urls:        # Only follow links beneath the base URL        # 如果鏈接是以傳入的url開始則放入隊(duì)列        if new_url.startswith(base_url):          yield q.put(new_url)    finally:      # 隊(duì)列內(nèi)數(shù)據(jù)減一      q.task_done()  @gen.coroutine  def worker():    while True:      # 保證程序持續(xù)運(yùn)行      yield fetch_url()  # 將第一個(gè)url放入隊(duì)列  q.put(base_url)  # Start workers, then wait for the work queue to be empty.  for _ in range(concurrency):    # 啟動(dòng)對應(yīng)數(shù)量的worker    worker()  # 等待隊(duì)列數(shù)據(jù)處理完成  yield q.join(timeout=timedelta(seconds=300))  # 如果兩個(gè)集合不相等拋出異常  assert fetching == fetched  # 打印執(zhí)行時(shí)間  print('Done in %d seconds, fetched %s URLs.' % (    time.time() - start, len(fetched)))if __name__ == '__main__':  io_loop = ioloop.IOLoop.current()  io_loop.run_sync(main)