Python爬虫(十八)_多线程糗事百科案例

2018-02-27 11:10:20来源:https://www.jianshu.com/p/de2167b0b3bd作者:小七奇奇人点击

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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:http://www.cnblogs.com/miqi1992/p/8081929.html


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


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("String: "+self.threadID)
self.qiushi_spider()
print("Exiting: "+self.threadID)
def qiushi_spider(self):
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:
# 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].text
except:
pass
result = {
'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 += 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(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parseList
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_Parser
exitFlag_Parser = True
for t in parserthreads:
t.join()
print 'Exiting Main Thread'
with lock:
output.close()
if __name__ == '__main__':
main()



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