4.1 加速爬虫: 多进程分布式

首页中有很多url,使用多进程同时开始下载这些url,得到这些 url 的HTML以后, 同时开始解析网页内容. 在网页中寻找这个网站还没有爬过的链接. 最终爬完整个莫烦Python网站所有页面

import multiprocessing as mp
import time
from urllib.request import urlopen, urljoin
from bs4 import BeautifulSoup
import re


base_url = 'https://morvanzhou.github.io/'

def crawl(url):
    response = urlopen(url)
    time.sleep(0.1)             # slightly delay for downloading
    return response.read().decode()


def parse(html):
    soup = BeautifulSoup(html, 'lxml')
    urls = soup.find_all('a', {"href": re.compile('^/.+?/$')})
    title = soup.find('h1').get_text().strip()
    page_urls = set([urljoin(base_url, url['href']) for url in urls])
    url = soup.find('meta', {'property': "og:url"})['content']
    return title, page_urls, url

unseen = set([base_url,])
seen = set()

count, t1 = 1, time.time()

while len(unseen) != 0:                 # still get some url to visit
    if len(seen) > 20:
            break

    print('\nDistributed Crawling...')
    htmls = [crawl(url) for url in unseen]

    print('\nDistributed Parsing...')
    results = [parse(html) for html in htmls]

    print('\nAnalysing...')
    seen.update(unseen)         # seen the crawled
    unseen.clear()              # nothing unseen

    for title, page_urls, url in results:
        print(count, title, url)
        count += 1
        unseen.update(page_urls - seen)     # get new url to crawl
print('Total time: %.1f s' % (time.time()-t1, ))    # 53 s

if __name__ == '__main__':
    unseen = set([base_url,])
    seen = set()

    pool = mp.Pool(4)                       
    count, t1 = 1, time.time()
    while len(unseen) != 0:                 # still get some url to visit
        if len(seen) > 20:
                break
        print('\nDistributed Crawling...')
        crawl_jobs = [pool.apply_async(crawl, args=(url,)) for url in unseen]
        htmls = [j.get() for j in crawl_jobs]                                       # request connection

        print('\nDistributed Parsing...')
        parse_jobs = [pool.apply_async(parse, args=(html,)) for html in htmls]
        results = [j.get() for j in parse_jobs]                                     # parse html

        print('\nAnalysing...')
        seen.update(unseen)         # seen the crawled
        unseen.clear()              # nothing unseen

        for title, page_urls, url in results:
            print(count, title, url)
            count += 1
            unseen.update(page_urls - seen)     # get new url to crawl
    print('Total time: %.1f s' % (time.time()-t1, ))    # 16 s !!!