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简易多线程爬虫框架

本文首发于知乎

本文使用多线程实现一个简易爬虫框架,让我们只需要关注网页的解析,不用自己设置多线程、队列等事情。调用形式类似scrapy,而诸多功能还不完善,因此称为简易爬虫框架。

这个框架实现了Spider类,让我们只需要写出下面代码,即可多线程运行爬虫

class DouBan(Spider):

    def __init__(self):
        super(DouBan, self).__init__()
        self.start_url = 'https://movie.douban.com/top250'
        self.filename = 'douban.json' # 覆盖默认值
        self.output_result = False 
        self.thread_num = 10

    def start_requests(self): # 覆盖默认函数
        yield (self.start_url, self.parse_first)

    def parse_first(self, url): # 只需要yield待爬url和回调函数
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')

        movies = soup.find_all('div', class_ = 'info')[:5]
        for movie in movies:
            url = movie.find('div', class_ = 'hd').a['href']
            yield (url, self.parse_second)

        nextpage = soup.find('span', class_ = 'next').a
        if nextpage:
            nexturl = self.start_url + nextpage['href']
            yield (nexturl, self.parse_first)
        else:
            self.running = False # 表明运行到这里则不会继续添加待爬URL队列

    def parse_second(self, url):
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')
        mydict = {}
        title = soup.find('span', property = 'v:itemreviewed')
        mydict['title'] = title.text if title else None
        duration = soup.find('span', property = 'v:runtime')
        mydict['duration'] = duration.text if duration else None
        time = soup.find('span', property = 'v:initialReleaseDate')
        mydict['time'] = time.text if time else None
        yield mydict


if __name__ == '__main__':
    douban = DouBan()
    douban.run()
复制代码

可以看到这个使用方式和scrapy非常相似

  • 继承类,只需要写解析函数(因为是简易框架,因此还需要写请求函数)
  • 用yield返回数据或者新的请求及回调函数
  • 自动多线程(scrapy是异步)
  • 运行都一样只要run
  • 可以设置是否存储到文件等,只是没有考虑可扩展性(数据库等)

下面我们来说一说它是怎么实现的

我们可以对比下面两个版本,一个是上一篇文章中的使用方法,另一个是进行了一些修改,将一些功能抽象出来,以便扩展功能。

上一篇文章版本代码请读者自行点击链接去看,下面是修改后的版本代码。

import requests
import time
import threading
from queue import Queue, Empty
import json
from bs4 import BeautifulSoup

def run_time(func):
    def wrapper(*args, **kw):
        start = time.time()
        func(*args, **kw)
        end = time.time()
        print('running', end-start, 's')
    return wrapper


class Spider():

    def __init__(self):
        self.start_url = 'https://movie.douban.com/top250'
        self.qtasks = Queue()
        self.data = list()
        self.thread_num = 5
        self.running = True

    def start_requests(self):
        yield (self.start_url, self.parse_first)

    def parse_first(self, url):
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')

        movies = soup.find_all('div', class_ = 'info')[:5]
        for movie in movies:
            url = movie.find('div', class_ = 'hd').a['href']
            yield (url, self.parse_second)

        nextpage = soup.find('span', class_ = 'next').a
        if nextpage:
            nexturl = self.start_url + nextpage['href']
            yield (nexturl, self.parse_first)
        else:
            self.running = False


    def parse_second(self, url):
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')
        mydict = {}
        title = soup.find('span', property = 'v:itemreviewed')
        mydict['title'] = title.text if title else None
        duration = soup.find('span', property = 'v:runtime')
        mydict['duration'] = duration.text if duration else None
        time = soup.find('span', property = 'v:initialReleaseDate')
        mydict['time'] = time.text if time else None
        yield mydict


    def start_req(self):
        for task in self.start_requests():
            self.qtasks.put(task)

    def parses(self):
        while self.running or not self.qtasks.empty():
            try:
                url, func = self.qtasks.get(timeout=3)
                print('crawling', url)
                for task in func(url):
                    if isinstance(task, tuple):
                        self.qtasks.put(task)
                    elif isinstance(task, dict):
                        self.data.append(task)
                    else:
                        raise TypeError('parse functions have to yield url-function tuple or data dict')
            except Empty:
                print('{}: Timeout occurred'.format(threading.current_thread().name))
        print(threading.current_thread().name, 'finished')


    @run_time
    def run(self, filename=False):
        ths = []

        th1 = threading.Thread(target=self.start_req)
        th1.start()
        ths.append(th1)

        for _ in range(self.thread_num):
            th = threading.Thread(target=self.parses)
            th.start()
            ths.append(th)

        for th in ths:
            th.join()

        if filename:
            s = json.dumps(self.data, ensure_ascii=False, indent=4)
            with open(filename, 'w', encoding='utf-8') as f:
                f.write(s)

        print('Data crawling is finished.')

if __name__ == '__main__':
    Spider().run(filename='frame.json')
复制代码

这个改进主要思路如下

  • 我们希望写解析函数时,像scrapy一样,用yield返回待抓取的URL和它对应的解析函数,于是就做了一个包含(URL,解析函数)的元组队列,之后只要不断从队列中获取元素,用函数解析url即可,这个提取的过程使用多线程
  • yield可以返回两种类型数据,一种是元组(URL,解析函数),一种是字典(即我们要的数据),通过判断分别加入不同队列中。元组队列是不断消耗和增添的过程,而字典队列是一只增加,最后再一起输出到文件中
  • queue.get时,加入了timeout参数并做异常处理,保证每一个线程都能结束

这里其实没有特别的知识,也不需要解释很多,读者自己复制代码到文本文件里对比就知道了

然后框架的形式就是从第二种中,剥离一些通用的设定,让用户自定义每个爬虫独特的部分,完整代码如下(本文开头的代码就是下面这块代码的后半部分)

import requests
import time
import threading
from queue import Queue, Empty
import json
from bs4 import BeautifulSoup

def run_time(func):
    def wrapper(*args, **kw):
        start = time.time()
        func(*args, **kw)
        end = time.time()
        print('running', end-start, 's')
    return wrapper


class Spider():

    def __init__(self):
        self.qtasks = Queue()
        self.data = list()
        self.thread_num = 5
        self.running = True
        self.filename = False
        self.output_result = True

    def start_requests(self):
        yield (self.start_url, self.parse)

    def start_req(self):
        for task in self.start_requests():
            self.qtasks.put(task)

    def parses(self):
        while self.running or not self.qtasks.empty():
            try:
                url, func = self.qtasks.get(timeout=3)
                print('crawling', url)
                for task in func(url):
                    if isinstance(task, tuple):
                        self.qtasks.put(task)
                    elif isinstance(task, dict):
                        if self.output_result:
                            print(task)
                        self.data.append(task)
                    else:
                        raise TypeError('parse functions have to yield url-function tuple or data dict')
            except Empty:
                print('{}: Timeout occurred'.format(threading.current_thread().name))
        print(threading.current_thread().name, 'finished')

    @run_time
    def run(self):
        ths = []

        th1 = threading.Thread(target=self.start_req)
        th1.start()
        ths.append(th1)

        for _ in range(self.thread_num):
            th = threading.Thread(target=self.parses)
            th.start()
            ths.append(th)

        for th in ths:
            th.join()

        if self.filename:
            s = json.dumps(self.data, ensure_ascii=False, indent=4)
            with open(self.filename, 'w', encoding='utf-8') as f:
                f.write(s)

        print('Data crawling is finished.')



class DouBan(Spider):

    def __init__(self):
        super(DouBan, self).__init__()
        self.start_url = 'https://movie.douban.com/top250'
        self.filename = 'douban.json' # 覆盖默认值
        self.output_result = False 
        self.thread_num = 10

    def start_requests(self): # 覆盖默认函数
        yield (self.start_url, self.parse_first)

    def parse_first(self, url): # 只需要yield待爬url和回调函数
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')

        movies = soup.find_all('div', class_ = 'info')[:5]
        for movie in movies:
            url = movie.find('div', class_ = 'hd').a['href']
            yield (url, self.parse_second)

        nextpage = soup.find('span', class_ = 'next').a
        if nextpage:
            nexturl = self.start_url + nextpage['href']
            yield (nexturl, self.parse_first)
        else:
            self.running = False # 表明运行到这里则不会继续添加待爬URL队列

    def parse_second(self, url):
        r = requests.get(url)
        soup = BeautifulSoup(r.content, 'lxml')
        mydict = {}
        title = soup.find('span', property = 'v:itemreviewed')
        mydict['title'] = title.text if title else None
        duration = soup.find('span', property = 'v:runtime')
        mydict['duration'] = duration.text if duration else None
        time = soup.find('span', property = 'v:initialReleaseDate')
        mydict['time'] = time.text if time else None
        yield mydict


if __name__ == '__main__':
    douban = DouBan()
    douban.run()
复制代码

我们这样剥离之后,就只需要写后半部分的代码,只关心网页的解析,不用考虑多线程的实现了。

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