前言
本节开始学习scrapy
1、原理
Scrapy主要包括了以下组件：
- 引擎(Scrapy)：用来处理整个系统的数据流处理, 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, 由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运行流程大概如下：
- 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
2、命令行
#1.创建一个新的项目
scrapy startproject [项目名]
#2.生成爬虫
scrapy genspider +文件名+网址
#3.运行(crawl)
scrapy crawl +爬虫名称
scrapy crawl [爬虫名] -o zufang.json
# -o output
scrapy crawl [爬虫名] -o zufang.csv
#4.check检查错误
scrapy check
#5.list返回项目所有spider名称
scrapy list
#6. view 存储、打开网页
scrapy view https://www.baidu.com
#7. scrapy shell，进入终端
scrapy shell https://www.baidu.co
#8. scrapy runspider
scrapy runspider zufang_spider.py3、一个简单例子
爬取租房信息
items.py
import scrapy
class MaitianItem(scrapy.Item):
# define the fields for your item here like:
# name = scrapy.Field()
title = scrapy.Field()
price = scrapy.Field()
area = scrapy.Field()
district = scrapy.Field()settings.py
BOT_NAME = 'maitian'
SPIDER_MODULES = ['maitian.spiders']
NEWSPIDER_MODULE = 'maitian.spiders'
ROBOTSTXT_OBEY = True
TEM_PIPELINES = {'maitian.pipelines.MaitianPipeline': 300,}
MONGODB_HOST = '127.0.0.1'
MONGODB_PORT = 27017
MONGODB_DBNAME = 'maitian'
MONGODB_DOCNAME = 'zufang'pipelines.py
import pymongo
from scrapy.conf import settings
class MaitianPipeline(object):
def __init__(self):
host = settings['MONGODB_HOST']
port = settings['MONGODB_PORT']
db_name = settings['MONGODB_DBNAME']
client = pymongo.MongoClient(host=host, port=port)
db = client[db_name]
self.post = db[settings['MONGODB_DOCNAME']]
# 数据持久化
def process_item(self, item, spider):
zufang = dict(item)
self.post.insert(zufang)
return itemmiddlewares.py
from scrapy import signals
class MaitianSpiderMiddleware(object):
# 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.
@classmethod
def from_crawler(cls, crawler):
# This method is used by Scrapy to create your spiders.
s = cls()
crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
return s
def 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 None
def 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, dict or Item objects.
for i in result:
yield i
def 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 Response, dict
# or Item objects.
pass
def 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 r
def spider_opened(self, spider):
spider.logger.info('Spider opened: %s' % spider.name)
class MaitianDownloaderMiddleware(object):
# 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.
@classmethod
def from_crawler(cls, crawler):
# This method is used by Scrapy to create your spiders.
s = cls()
crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
return s
def 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 called
return None
def 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 IgnoreRequest
return response
def 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() chain
pass
def spider_opened(self, spider):
spider.logger.info('Spider opened: %s' % spider.name)zufang_spider.py
import scrapy
from maitian.items import MaitianItem
class MaitianSpider(scrapy.Spider):
name = "zufang"
start_urls = ['http://bj.maitian.cn/zfall/PG1'] #起始url
def parse(self, response): #解析函数parse
for zufang_item in response.xpath('//div[@class="list_title"]'):
yield {
'title': zufang_item.xpath('./h1/a/text()').extract_first().strip(),
'price': zufang_item.xpath('./div[@class="the_price"]/ol/strong/span/text()').extract_first().strip(),
'area': zufang_item.xpath('./p/span/text()').extract_first().replace('㎡','')
.strip(),
'district': zufang_item.xpath('./p//text()').re(r'昌平|朝阳|东城|大兴|丰台|海淀|石景山|顺义|通州|西城')[0],
}
next_page_url = response.xpath('//div[@id="paging"]/a[@class="down_page"]/@href').extract_first() #下一页
if next_page_url is not None:
yield scrapy.Request(response.urljoin(next_page_url))结语
简单感受了下scrapy
之后慢慢学习