python使用tornado实现简单爬虫

本文实例为大家分享了python使用tornado实现简单爬虫的具体代码，供大家参考，具体内容如下

代码在官方文档的示例代码中有,但是作为一个tornado新手来说阅读起来还是有点困难的,于是我在代码中添加了注释,方便理解,代码如下:

# coding=utf-8
 #!/usr/bin/env python

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

 # 设置要爬取的网址
base_url = 'http://www.baidu.com'
 # 设置worker数量
concurrency = 10
 # 此代码会获取base_url下的所有其他url
@gen.coroutine
def get_links_from_url(url):

  try:
    # 通过异步向url发起请求
    response = yield httpclient.AsyncHTTPClient().fetch(url)
    print('fetched %s' % url)
    # 响应如果是字节类型 进行解码
    html = response.body if isinstance(response.body, str) \
      else response.body.decode(errors='ignore')
    # 构建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))
    # 报错返回空列表
    raise gen.Return([])
  # 返回url列表
  raise gen.Return(urls)


def remove_fragment(url):
  #去除锚点
  pure_url, frag = urldefrag(url)

  return pure_url


def get_links(html):
  #从html页面里提取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.coroutine
def main():
  # 创建队列
  q = queues.Queue()
  # 记录开始时间戳
  start = time.time()
  # 构建两个集合
  fetching, fetched = set(), set()

  @gen.coroutine
  def fetch_url():
    # 从队列中取出数据
    current_url = yield q.get()
    try:
      # 如果取出的数据在队列中已经存在 返回
      if current_url in fetching:
        return

      print('fetching %s' % current_url)
      # 如果不存在添加到集合当中
      fetching.add(current_url)
      # 从新放入的链接中继续获取链接
      urls = yield get_links_from_url(current_url)
      # 将已经请求玩的url放入第二个集合
      fetched.add(current_url)

      for new_url in urls:
        # Only follow links beneath the base URL
        # 如果链接是以传入的url开始则放入队列
        if new_url.startswith(base_url):
          yield q.put(new_url)

    finally:
      # 队列内数据减一
      q.task_done()

  @gen.coroutine
  def worker():
    while True:
      # 保证程序持续运行
      yield fetch_url()
  # 将第一个url放入队列
  q.put(base_url)

  # Start workers, then wait for the work queue to be empty.
  for _ in range(concurrency):
    # 启动对应数量的worker
    worker()
  # 等待队列数据处理完成
  yield q.join(timeout=timedelta(seconds=300))
  # 如果两个集合不相等抛出异常
  assert fetching == fetched
  # 打印执行时间
  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)