做现货IC电子网站的,网站热图分析,中国志愿者服务网站登录注册,建立一个公司网站大约多少钱scrapy的入门使用
学习目标#xff1a;
掌握 scrapy的安装应用 创建scrapy的项目应用 创建scrapy爬虫应用 运行scrapy爬虫应用 scrapy定位以及提取数据或属性值的方法掌握 response响应对象的常用属性 1 安装scrapy
命令: sudo apt-get install scrapy 或者#x…scrapy的入门使用
学习目标
掌握 scrapy的安装应用 创建scrapy的项目应用 创建scrapy爬虫应用 运行scrapy爬虫应用 scrapy定位以及提取数据或属性值的方法掌握 response响应对象的常用属性 1 安装scrapy
命令: sudo apt-get install scrapy 或者 pip/pip3 install scrapy
2 scrapy项目开发流程
创建项目: scrapy startproject mySpider生成一个爬虫: scrapy genspider lianjia lianjia.com提取数据: 根据网站结构在spider中实现数据采集相关内容保存数据: 使用pipeline进行数据后续处理和保存
3. 创建项目 通过命令将scrapy项目的的文件生成出来后续步骤都是在项目文件中进行相关操作下面以抓取传智师资库来学习scrapy的入门使 创建scrapy项目的命令 scrapy startproject 项目名字 示例 scrapy startproject myspider
生成的目录和文件结果如下 对几个py文件做如下说明
items.py
# Define here the models for your scraped items# See documentation in:
# https://docs.scrapy.org/en/latest/topics/items.htmlimport scrapy# 实际是一个模板类 主要是用来定义数据存储模型
# 通过这个类实例化 数据实际存到实例对象中
class MyspiderItem(scrapy.Item):# 实际是一个模板类数据建模 事先定义好你要爬取的字段name scrapy.Field() # 租房标题content scrapy.Field() # 详情信息price scrapy.Field() # 价格link scrapy.Field() # 详情链接
middlewares.py 用于编写中间件下载中间件爬虫中间件 – 无特殊需求一般不需要编写 Define here the models for your spider middleware
#
# See documentation in:
# https://docs.scrapy.org/en/latest/topics/spider-middleware.htmlfrom scrapy import signals# useful for handling different item types with a single interface
from itemadapter import is_item, ItemAdapterclass MyspiderSpiderMiddleware:# Not all methods need to be defined. If a method is not defined,# scrapy acts as if the spider middleware does not modify the# passed objects.classmethoddef from_crawler(cls, crawler):# This method is used by Scrapy to create your spiders.s cls()crawler.signals.connect(s.spider_opened, signalsignals.spider_opened)return sdef process_spider_input(self, response, spider):# Called for each response that goes through the spider# middleware and into the spider.# Should return None or raise an exception.return Nonedef process_spider_output(self, response, result, spider):# Called with the results returned from the Spider, after# it has processed the response.# Must return an iterable of Request, or item objects.for i in result:yield idef process_spider_exception(self, response, exception, spider):# Called when a spider or process_spider_input() method# (from other spider middleware) raises an exception.# Should return either None or an iterable of Request or item objects.passdef process_start_requests(self, start_requests, spider):# Called with the start requests of the spider, and works# similarly to the process_spider_output() method, except# that it doesn’t have a response associated.# Must return only requests (not items).for r in start_requests:yield rdef spider_opened(self, spider):spider.logger.info(Spider opened: %s % spider.name)class MyspiderDownloaderMiddleware:# Not all methods need to be defined. If a method is not defined,# scrapy acts as if the downloader middleware does not modify the# passed objects.classmethoddef from_crawler(cls, crawler):# This method is used by Scrapy to create your spiders.s cls()crawler.signals.connect(s.spider_opened, signalsignals.spider_opened)return sdef process_request(self, request, spider):# Called for each request that goes through the downloader# middleware.# Must either:# - return None: continue processing this request# - or return a Response object# - or return a Request object# - or raise IgnoreRequest: process_exception() methods of# installed downloader middleware will be calledreturn Nonedef process_response(self, request, response, spider):# Called with the response returned from the downloader.# Must either;# - return a Response object# - return a Request object# - or raise IgnoreRequestreturn responsedef process_exception(self, request, exception, spider):# Called when a download handler or a process_request()# (from other downloader middleware) raises an exception.# Must either:# - return None: continue processing this exception# - return a Response object: stops process_exception() chain# - return a Request object: stops process_exception() chainpassdef spider_opened(self, spider):spider.logger.info(Spider opened: %s % spider.name)
pipelines.py 管道 – 主要用于编写数据处理步骤 数据的清洗保存
# Define your item pipelines here# Dont forget to add your pipeline to the ITEM_PIPELINES setting
# See: https://docs.scrapy.org/en/latest/topics/item-pipeline.html# useful for handling different item types with a single interface
from itemadapter import ItemAdapterclass MyspiderPipeline:def process_item(self, itemder):return item
settings.py 详细的配置信息设置文件 UA 启动管道 Scrapy settings for mySpider project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
# https://docs.scrapy.org/en/latest/topics/settings.html
# https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
# https://docs.scrapy.org/en/latest/topics/spider-middleware.htmlBOT_NAME mySpiderSPIDER_MODULES [mySpider.spiders]
NEWSPIDER_MODULE mySpider.spiders# Crawl responsibly by identifying yourself (and your website) on the user-agent
# 需要手动修改成自己浏览器的UA
USER_AGENT mySpider (http://www.yourdomain.com)# Obey robots.txt rules
ROBOTSTXT_OBEY False # 需要手动修改为False# 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://docs.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:
# 可以写入一些爬虫所需要的身份信息
#DEFAULT_REQUEST_HEADERS {
# Accept: text/html,application/xhtmlxml,application/xml;q0.9,*/*;q0.8,
# Accept-Language: en,
#}# Enable or disable spider middlewares
# See https://docs.scrapy.org/en/latest/topics/spider-middleware.html
# SPIDER_MIDDLEWARES {
# mySpider.middlewares.MyspiderSpiderMiddleware: 543,
# }# Enable or disable downloader middlewares
# See https://docs.scrapy.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES {
# mySpider.middlewares.MyspiderDownloaderMiddleware: 543,
#}# Enable or disable extensions
# See https://docs.scrapy.org/en/latest/topics/extensions.html
#EXTENSIONS {
# scrapy.extensions.telnet.TelnetConsole: None,
#}# Configure item pipelines
# See https://docs.scrapy.org/en/latest/topics/item-pipeline.html
# 开启管道类才能写入数据
ITEM_PIPELINES {mySpider.pipelines.MyspiderPipeline: 300,
}# Enable and configure the AutoThrottle extension (disabled by default)
# See https://docs.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://docs.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. 创建爬虫 通过命令创建出爬虫文件爬虫文件为主要的代码作业文件通常一个网站的爬取动作都会在爬虫文件中进行编写。 命令 在项目路径下执行: scrapy genspider 爬虫名字 允许爬取的域名
爬虫名字: 作为爬虫运行时的参数 允许爬取的域名: 为对于爬虫设置的爬取范围设置之后用于过滤要爬取的url如果爬取的url与允许的域不通则被过滤掉。
示例 cd myspiderscrapy genspider itcast itcast.cn生成的目录和文件结果如下 5. 完善爬虫 在上一步生成出来的爬虫文件中编写指定网站的数据采集操作实现数据提取 5.1 在/myspider/myspider/spiders/itcast.py中修改内容如下:
import scrapyclass ItcastSpider(scrapy.Spider): # 继承scrapy.spider# 爬虫名字 name itcast # 允许爬取的范围allowed_domains [itcast.cn] # 开始爬取的url地址start_urls [http://www.itcast.cn/channel/teacher.shtml]# 数据提取的方法接受下载中间件传过来的responsedef parse(self, response): # scrapy的response对象可以直接进行xpathnames response.xpath(//div[classtea_con]//li/div/h3/text()) print(names)# 获取具体数据文本的方式如下# 分组li_list response.xpath(//div[classtea_con]//li) for li in li_list:# 创建一个数据字典item {}# 利用scrapy封装好的xpath选择器定位元素并通过extract()或extract_first()来获取结果# extract_first()如果没结果就返回None 值只有一个的时候可以选择该方法item[name] li.xpath(.//h3/text()).sc_first() # 老师的名字item[level] li.xpath(.//h4/text()).extract_first() # 老师的级别item[text] li.xpath(.//p/text()).extract_first() # 老师的介绍print(item)# 使用yield返回数据yield temp 注意
scrapy.Spider爬虫类中必须有名为parse的解析如果网站结构层次比较复杂也可以自定义其他解析函数在解析函数中提取的url地址如果要发送请求则必须属于allowed_domains范围内但是start_urls中的url地址不受这个限制我们会在后续的课程中学习如何在解析函数中构造发送请求启动爬虫的时候注意启动的位置是在项目路径下启动parse()函数中使用yield返回数据注意解析函数中的yield能够传递的对象只能是BaseItem, Request, dict, None
5.2 定位元素以及提取数据、属性值的方法 解析并获取scrapy爬虫中的数据: 利用xpath规则字符串进行定位和提取 response.xpath方法的返回结果是一个类似list的类型其中包含的是selector对象操作和列表一样但是有一些额外的方法额外方法extract()返回一个包含有字符串的列表额外方法extract_first()返回列表中的第一个字符串列表为空没有返回None
5.3 response响应对象的常用属性
response.url当前响应的url地址response.request.url当前响应对应的请求的url地址response.headers响应头response.requests.headers当前响应的请求头response.body响应体也就是html代码byte类型response.status响应状态码
6 保存数据 利用管道pipeline来处理(保存)数据 6.1 在pipelines.py文件中定义对数据的操作
定义一个管道类重写管道类的process_item方法process_item方法处理完item之后必须返回给引擎
import jsonclass ItcastPipeline():# 爬虫文件中提取数据的方法每yield一次item就会运行一次# 该方法为固定名称函数def process_item(self, item, spider): # 参数item:是爬虫文件中yield的返回的数据对象引擎会把这个交给管道中的这个item参数print(item)return item # 默认使用完管道之后需要把数据返回给引擎6.2 在settings.py配置启用管道
ITEM_PIPELINES {# 目录文件 该值的大小决定管道执行的顺序值越小优先级越高该值最好 不要大于1000myspider.pipelines.lianjiaPipeline: 400
}配置项中键为使用的管道类管道类使用.进行分割第一个为项目目录第二个为文件第三个为定义的管道类。 配置项中值为管道的使用顺序设置的数值约小越优先执行该值一般设置为1000以内。
7. 运行scrapy
命令在项目目录下执行scrapy crawl 爬虫名字
示例r 【scrapy crawl itcast --nolog 忽略日志信息】 小结
scrapy的安装pip install scrapy创建scrapy的项目: scrapy startproject myspider创建scrapy爬虫在项目目录下执行 scrapy genspider itcast itcast.cn运行scrapy爬虫在项目目录下执行 scrapy crawl itcast 【scrapy crawl itcast --nolog 忽略日志信息】解析并获取scrapy爬虫中的数据 response.xpath方法的返回结果是一个类似list的类型其中包含的是selector对象操作和列表一样但是有一些额外的方法extract() 返回一个包含有字符串的列表extract_first() 返回列表中的第一个字符串列表为空没有返回None scrapy管道的基本使用: 完善pipelines.py中的process_item函数在settings.py中设置开启pipeline response响应对象的常用属性 response.url当前响应的url地址response.request.url当前响应对应的请求的url地址response.headers响应头response.requests.headers当前响应的请求头response.body响应体也就是html代码byte类型response.status响应状态码
