[scrapy]Item Loders

Items

Items就是结构化数据的模块,相当于字典,比如定义一个{"title":"","author":""},items_loders就是从网页中提取title和author字段填充到items里,比如{"title":"初学scrapy","author":"Alex"},然后items把结构化的数据传给pipeline,pipeline可以把数据插入进MySQL里.

实例

items.py

import scrapy


class JobBoleArticleItem(scrapy.Item):
    title = scrapy.Field()
    create_date = scrapy.Field()
    url = scrapy.Field()
    url_object_id = scrapy.Field()
    front_image_url = scrapy.Field()
    front_image_path = scrapy.Field()
    praise_nums = scrapy.Field()
    comment_nums = scrapy.Field()
    fav_nums = scrapy.Field()

jobbole.py

# -*- coding: utf-8 -*-
import scrapy
from scrapy.http import Request
from scrapy.loader import ItemLoader

from urllib import parse
import re
import  datetime
from ArticleSpider.items import JobBoleArticleItem

from utils.common import get_md5

class JpbboleSpider(scrapy.Spider):
    name = 'jobbole'
    allowed_domains = ['blog.jobbole.com']
    start_urls = ['http://blog.jobbole.com/all-posts/']  #先下载http://blog.jobbole.com/all-posts/这个页面,然后传给parse解析

    def parse(self, response):

        #1.start_urls下载页面http://blog.jobbole.com/all-posts/,然后交给parse解析,parse里的post_urls获取这个页面的每个文章的url,Request下载每个文章的页面,然后callback=parse_detail,交给parse_detao解析
        #2.等post_urls这个循环执行完,说明这一个的每个文章都已经解析完了, 就执行next_url,next_url获取下一页的url,然后Request下载,callback=self.parse解析,parse从头开始,先post_urls获取第二页的每个文章的url,然后循环每个文章的url,交给parse_detail解析

        #获取http://blog.jobbole.com/all-posts/中所有的文章url,并交给Request去下载,然后callback=parse_detail,交给parse_detail解析
        post_nodes = response.css("#archive  .floated-thumb .post-thumb a")
        for post_node in post_nodes:
            image_url = post_node.css("img::attr(src)").extract_first("")
            post_url = post_node.css("::attr(href)").extract_first("")
            yield Request(url=parse.urljoin(response.url,post_url),meta={"front_image_url":image_url},callback=self.parse_detail)

        #获取下一页的url地址,交给Request下载,然后交给parse解析
        next_url = response.css(".next.page-numbers::attr(href)").extract_first("")
        if next_url:
            yield Request(url=next_url,callback=self.parse)

    def parse_detail(self,response):

        article_item = JobBoleArticleItem()  #实例化定义的items
    
        item_loader = ItemLoader(item=JobBoleArticleItem(),response=response) #实例化item_loader,把我们定义的item传进去,再把下载器下载的网页穿进去
        #针对直接取值的情况
        item_loader.add_value("url",response.url)
        item_loader.add_value("url_object_id",get_md5(response.url))
        item_loader.add_value("front_image_url",[front_image_url])
        #针对css选择器
        item_loader.add_css("title",".entry-header h1::text")
        item_loader.add_css("create_date","p.entry-meta-hide-on-mobile::text")
        item_loader.add_css("praise_nums",".vote-post-up h10::text")
        item_loader.add_css("comment_nums","a[href='#article-comment'] span::text")
        item_loader.add_css("fav_nums",".bookmark-btn::text")
        #把结果返回给items
        article_item = item_loader.load_item()


    　　

• .add_value:把直接获取到的值,复制给字段
• .add_css:需要通过css选择器获取到的值
• .add_xpath:需要通过xpath选择器获取到的值

debug调试,可以看到拿到的信息