爬虫之多线程案例

Posted 2020-09-02 林深时见鹿

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

Queue（队列对象）

Queue是python中的标准库，可以直接import Queue引用;队列是线程间最常用的交换数据的形式

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

1. 初始化： class Queue.Queue(maxsize) FIFO 先进先出

2. 包中的常用方法:

   • Queue.qsize() 返回队列的大小

   • Queue.empty() 如果队列为空，返回True,反之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等待时间

3. 创建一个“队列”对象

   • import Queue
   • myqueue = Queue.Queue(maxsize = 10)

4. 将一个值放入队列中

   • myqueue.put(10)

5. 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 json


class thread_crawl(threading.Thread):
    \'\'\'
    抓取线程类
    \'\'\'

    def __init__(self, threadID, q):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.q = q

    def run(self):
        print "Starting " + self.threadID
        self.qiushi_spider()
        print "Exiting ", self.threadID

    def qiushi_spider(self):
        # page = 1
        while True:
            if self.q.empty():
                break
            else:
                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 = 4
                while timeout > 0:
                    timeout -= 1
                    try:
                        content = requests.get(url, headers=headers)
                        data_queue.put(content.text)
                        break
                    except Exception, e:
                        print \'qiushi_spider\', e
                if timeout < 0:
                    print \'timeout\', url


class Thread_Parser(threading.Thread):
    \'\'\'
    页面解析类；
    \'\'\'

    def __init__(self, threadID, queue, lock, f):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.queue = queue
        self.lock = lock
        self.f = f

    def run(self):
        print \'starting \', self.threadID
        global total, exitFlag_Parser
        while 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:
                    pass
                self.parse_data(item)
                self.queue.task_done()
                print \'Thread_Parser=\', self.threadID, \',total=\', total
            except:
                pass
        print \'Exiting \', self.threadID

    def parse_data(self, item):
        \'\'\'
        解析网页函数
        :param item: 网页内容
        :return:
        \'\'\'
        global total
        try:
            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].text
                    content = site.xpath(\'.//div[@class="content"]/span\')[0].text.strip()
                    vote = None
                    comments = None
                    try:
                        vote = site.xpath(\'.//i\')[0].text
                        comments = site.xpath(\'.//i\')[1].text
                    except:
                        pass
                    result = {
                        \'imgUrl\': imgUrl,
                        \'title\': title,
                        \'content\': content,
                        \'vote\': vote,
                        \'comments\': comments,
                    }

                    with self.lock:
                        # print \'write %s\' % json.dumps(result)
                        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 += 1

data_queue = Queue()
exitFlag_Parser = False
lock = threading.Lock()
total = 0

def main():
    output = open(\'qiushibaike.json\', \'a\')

    #初始化网页页码page从1-10个页面
    pageQueue = Queue(50)
    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parserList
    parserthreads = []
    parserList = ["parser-1", "parser-2", "parser-3"]
    #分别启动parserList
    for threadID in parserList:
        thread = Thread_Parser(threadID, data_queue, lock, output)
        thread.start()
        parserthreads.append(thread)

    # 等待队列清空
    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
    # 通知线程是时候退出
    global exitFlag_Parser
    exitFlag_Parser = True

    for t in parserthreads:
        t.join()
    print "Exiting Main Thread"
    with lock:
        output.close()


if __name__ == \'__main__\':
    main()