Python爬虫(十八)_多线程糗事百科案例

多线程糗事百科案例

案例要求参考上一个糗事百科单进程案例:https://cloud.tencent.com/developer/article/1021994

Queue(队列对象)

Queue是python中的标准库，可以直接import Queue引用；队列时线程间最常用的交互数据的形式。

python下多线程的思考 对于资源，加锁是个重要的环节。因为python原生的list,dict等，都是not thread safe的。而Queue,是线程安全的，因此在满足使用条件下，建议使用队列

初始化：class Queue.Queue(maxsize)FIFO先进先出
包中的常用方法：
- Queue.qszie()返回队列的大小
- Queue.empty()如果队列为空，返回True，否则返回False
- Queue.full()如果队列满了，返回True,反之False
- Queue.full 与 maxsize大小对应
- Queue.get([block[, timeout]])获取队列，timeout等待事件
创建一个"队列"对象
- import Queue
- myqueue = Queue.Queue(maxsize=10)
将一个值放入队列中
- myqueue.put(10)
将一个值从队列中取出
- myqueue.get()

多线程示意图

#-*- coding:utf-8 -*-import requests
from lxml import etree
from Queue import Queue
import threading
import time
import jsonclass Thread_crawl(threading.Thread):"""抓取线程类"""def __init__(self, threadID, q):threading.Thread.__init__(self)self.threadID = threadIDself.q = qdef run(self):print("String: "+self.threadID)self.qiushi_spider()print("Exiting: "+self.threadID)def qiushi_spider(self):while True:if self.q.empty():breakelse:page = self.q.get()print('qiushi_spider=', self.threadID, 'page=', str(page))url = 'http://www.qiushibaike.com/8hr/page/' + str(page)+"/"headers = {'User-Agent':'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36','Accept-Language':'zh-CN,zh;q=0.8'}#多次尝试失败结束，防止死循环timeout = 4while timeout > 0:timeout -= 1try:content = requests.get(url, headers = headers)data_queue.put(content.text)breakexcept Exception, e:print "qiushi_spider", eif timeout < 0:print 'timeout', urlclass Thread_Parser(threading.Thread):"""页面解析类"""def __init__(self, threadID, queue, lock, f):threading.Thread.__init__(self)self.threadID = threadIDself.queue = queueself.lock = lockself.f = fdef run(self):print("starting ", self.threadID)global total, exitFlag_Parserwhile not exitFlag_Parser:try:"""调用队列对象的get()方法从队头删除并返回一个项目。可选参数为block， 默认为True如果队列为空且block为True，get()就使调用线程暂停，直至有项目可用如果队列为空且block为False,队列将引发Empty异常"""item = self.queue.get(False)if not item:passself.parse_data(item)self.queue.task_done()print("Thread_Parser=", self.threadID, 'total=', total)except:passprint "Exiting ", self.threadIDdef parse_data(self, item):"""解析网页函数:param item:网页内容:return"""global totaltry:html = etree.HTML(item)result = html.xpath('//div[contains(@id,"qiushi_tag")]')for site in result:try:imgUrl = site.xpath('.//img/@src')[0]title = site.xpath('.//h2')[0].textcontent = site.xpath('.//div[@class="content"]/span')[0].text.strip()vote = Nonecomments = Nonetry:# 投票次数vote = site.xpath('.//i')[0].text# print(vote)#print site.xpath('.//*[@class="number"]')[0].text# 评论信息comments = site.xpath('.//i')[1].textexcept:passresult = {'imageUrl' : imgUrl,'title' : title,'content' : content,'vote' : vote,'comments' : comments}with self.lock:self.f.write(json.dumps(result, ensure_ascii=False).encode('utf-8') + '\n') except Exception, e:print("site in result ", e)except Exception, e:print("parse_data", e)with self.lock:total += 1data_queue = Queue()
exitFlag_Parser = False
lock = threading.Lock()
total = 0def main():output = open('qiushibaike.json', 'a')#初始化网页页码page从1-10个页面pageQueue = Queue(10)for page in range(1, 11):pageQueue.put(page)#初始化采集线程crawlthreads = []crawllist = ["crawl-1", "crawl-2", "crawl-3"]for threadID in crawllist:thread = Thread_crawl(threadID, pageQueue)thread.start()crawlthreads.append(thread)# #初始化解析线程parseListparserthreads = []parserList = ["parser-1", "parser-2", "parser-3"]#分别启动parserListfor threadID in parserList:thread = Thread_Parser(threadID, data_queue, lock, output)thread.start()parserthreads.append(thread)# 等待队列情况while not pageQueue.empty():pass#等待所有线程完成for t in crawlthreads:t.join()while not data_queue.empty():pass#通知线程退出global exitFlag_ParserexitFlag_Parser = Truefor t in parserthreads:t.join()print 'Exiting Main Thread'with lock:output.close()if __name__ == '__main__':main()