Python爬虫Scrapy入门

2021-05-21 11:02:59 浏览数 (1)

Scrapy组成

Scrapy是Python开发的一个快速、高层次的屏幕抓取和web抓取框架，用于抓取web站点并从页面中提取结构化的数据。

  • 引擎（Scrapy）：用来处理整个系统的数据流，触发事务（框架核心）。
  • 调度器（Scheduler）：用来接受引擎发过来的请求, 压入队列中, 并在引擎再次请求的时候返回. 可以想像成一个URL（抓取网页的网址或者说是链接）的优先队列, 它来决定下一个要抓取的网址是什么, 同时去除重复的网址
  • 下载器(Downloader)：用于下载网页内容,并将网页内容返回给蜘蛛(Scrapy下载器是建立在twisted这个高效的异步模型上的)
  • 爬虫(Spiders)：爬虫是主要干活的, 用于从特定的网页中提取自己需要的信息, 即所谓的实体(Item)。用户也可以从中提取出链接,让Scrapy继续抓取下一个页面
  • 项目管道(Pipeline)：负责处理爬虫从网页中抽取的实体，主要的功能是持久化实体、验证实体的有效性、清除不需要的信息。当页面被爬虫解析后，将被发送到项目管道，并经过几个特定的次序处理数据。
  • 下载器中间件(Downloader Middlewares)：位于Scrapy引擎和下载器之间的框架，主要是处理Scrapy引擎与下载器之间的请求及响应。
  • 爬虫中间件(Spider Middlewares)：介于Scrapy引擎和爬虫之间的框架，主要工作是处理蜘蛛的响应输入和请求输出。
  • 调度中间件(Scheduler Middewares)：介于Scrapy引擎和调度之间的中间件，从Scrapy引擎发送到调度的请求和响应。

Scrapy运行流程

  • 引擎从调度器中取出一个链接(URL)用于接下来的抓取
  • 引擎把URL封装成一个请求(Request)传给下载器
  • 下载器把资源下载下来，并封装成应答包(Response)
  • 爬虫解析Response
  • 解析出实体（Item）,则交给实体管道进行进一步的处理
  • 解析出的是链接（URL）,则把URL交给调度器等待抓取

Scrapy创建

安装好scrapy类库之后，就可以创建scrapy项目了，pycharm不能直接创建scrapy项目，必须通过命令行创建，打开pycharm的Terminal终端，输入scrapy startproject scrapy_demo命令。需要注意的是，环境变量必须要配好才能在cmd中显示scrapy命令.

对于Mac，由于Mac的python有多个版本，如果使用3.6的版本，不能直接在命令行运行scrapy，需要创建软链接（注意对应的版本）。

代码语言：javascript复制
ln -s /Library/Frameworks/Python.framework/Versions/3.6/bin/scrapy /usr/local/bin/scrapy

看到下面的信息则说明创建成功了。

此时可以看到项目自动创建了以下几个文件

  • scrapy.cfg: 项目的配置文件
  • scrapy_demo/ ：该项目的python模块，之后将在这里加入代码
  • items.py：项目中的items文件，用来定义我们要抓取的数据
  • middlewares.py：项目中的middlewares文件
  • pipelines.py：项目中的pipelines文件，用来对spider返回的item列表进行数据的保存等操作，可以写入文件或保存到数据库
  • setting.py：爬虫配置文件
  • spiders/：放置spider代码的目录（自己编写）

scrapy网站爬取

接下来，将对IEEE和arXiv网站进行爬虫，其中middlewares.py，__init__.py文件保持默认。

①根据网站内容在item.py中定义爬取的数据结构

Python

代码语言：javascript复制
# -*- coding: utf-8 -*-

# Define here the models for your scraped items
#
# See documentation in:
# https://doc.scrapy.org/en/latest/topics/items.html

# 在items.py文件中定义我们要抓取的数据

import scrapy


class ScrapyDemoItem(scrapy.Item):

    # define the fields for your item here like:
    title = scrapy.Field()
    authors = scrapy.Field()
    subjects = scrapy.Field()
    # year = scrapy.Field()
    # type = scrapy.Field()
    # publisher = scrapy.Field()

②在该目录的Spiders文件夹下面建立自己的爬虫

arXiv_Spider.py

需要注意的是难点是对于HTML元素的提取，此处不具体解释提取的代码如何编写。

Python

代码语言：javascript复制
import scrapy
import re
from scrapy_demo.items import ScrapyDemoItem


class arXivSpider(scrapy.Spider):
    name = "arXiv_Spider"
    allowed_domains = ["arxiv.org"]
    start_urls = ['https://arxiv.org/list/cs.AI/recent']

    def parse(self, response):

        # get num line
        num = response.xpath('//*[@id="dlpage"]/small[1]/text()[1]').extract()[0]
        # get max_index
        max_index = int(re.search(r'd ', num).group(0))
        for index in range(1, max_index   1):
            item = ScrapyDemoItem()
            # get title and clean data
            title = response.xpath('//*[@id="dlpage"]/dl/dd['   str(index)   ']/div/div[1]/text()').extract()
            # remove blank char
            title = [i.strip() for i in title]
            # remove blank str
            title = [i for i in title if i is not '']
            # insert title
            try:
                item['title'] = title[0]
            except IndexError:

                item['title'] = 'error'
            authors = ''
            # authors'  father node
            xpath_fa = '//*[@id="dlpage"]/dl/dd['   str(index)   ']/div/div[2]//a/text()'
            author_list = response.xpath(xpath_fa).getall()
            authors = str.join('', author_list)
            item['authors'] = authors

            item['subjects'] = response.xpath(
                'string(//*[@id="dlpage"]/dl/dd['   str(5)   ']/div/div[5]/span[2])').extract_first()

            yield item

③配置settings.py

即将一些注释吊的部分根据自己的需要去掉注释并补充，这里我注释了一下几个内容:

设置用户代理，可以多设置几个，反爬虫:

Python

代码语言：javascript复制
USER_AGENT = 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36'

pipelines需要增加：

Python

代码语言：javascript复制
ITEM_PIPELINES = { 'scrapy_demo.pipelines.ScrapyDemoPipeline': 300, }

完整的settings.py: Python

代码语言：javascript复制
# -*- coding: utf-8 -*-

# Scrapy settings for scrapy_demo project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
#     https://doc.scrapy.org/en/latest/topics/settings.html
#     https://doc.scrapy.org/en/latest/topics/downloader-middleware.html
#     https://doc.scrapy.org/en/latest/topics/spider-middleware.html

BOT_NAME = 'scrapy_demo'

SPIDER_MODULES = ['scrapy_demo.spiders']
NEWSPIDER_MODULE = 'scrapy_demo.spiders'


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'scrapy_demo ( http://www.yourdomain.com)'

USER_AGENT = 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36'


# Obey robots.txt rules
ROBOTSTXT_OBEY = True

# Configure maximum concurrent requests performed by Scrapy (default: 16)
#CONCURRENT_REQUESTS = 32

# Configure a delay for requests for the same website (default: 0)
# See https://doc.scrapy.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
#DOWNLOAD_DELAY = 3
# The download delay setting will honor only one of:
#CONCURRENT_REQUESTS_PER_DOMAIN = 16
#CONCURRENT_REQUESTS_PER_IP = 16

# Disable cookies (enabled by default)
#COOKIES_ENABLED = False

# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED = False

# Override the default request headers:
#DEFAULT_REQUEST_HEADERS = {
#   'Accept': 'text/html,application/xhtml xml,application/xml;q=0.9,*/*;q=0.8',
#   'Accept-Language': 'en',
#}

# Enable or disable spider middlewares
# See https://doc.scrapy.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'scrapy_demo.middlewares.ScrapyDemoSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See https://doc.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'scrapy_demo.middlewares.ScrapyDemoDownloaderMiddleware': 543,
#}

# Enable or disable extensions
# See https://doc.scrapy.org/en/latest/topics/extensions.html
#EXTENSIONS = {
#    'scrapy.extensions.telnet.TelnetConsole': None,
#}

# Configure item pipelines
# See https://doc.scrapy.org/en/latest/topics/item-pipeline.html
ITEM_PIPELINES = {
    'scrapy_demo.pipelines.ScrapyDemoPipeline': 300,
}

# Enable and configure the AutoThrottle extension (disabled by default)
# See https://doc.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True
# The initial download delay
#AUTOTHROTTLE_START_DELAY = 5
# The maximum download delay to be set in case of high latencies
#AUTOTHROTTLE_MAX_DELAY = 60
# The average number of requests Scrapy should be sending in parallel to
# each remote server
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG = False

# Enable and configure HTTP caching (disabled by default)
# See https://doc.scrapy.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
#HTTPCACHE_ENABLED = True
#HTTPCACHE_EXPIRATION_SECS = 0
#HTTPCACHE_DIR = 'httpcache'
#HTTPCACHE_IGNORE_HTTP_CODES = []
#HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'

④在终端运行爬虫文件

代码语言：javascript复制
scrapy crawl arXiv_Spider

结果：

爬虫 scrapy python php

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