python reptile - Picture lazily

Pictures lazy loading

    是一种反爬机制,图片懒加载是一种网页优化技术。图片作为一种网络资源，在被请求时也与普通静态资源一样，将占用网络资源，而一次性将整个页面的所有图片加载完，将大大增加页面的首屏加载时间。为了解决这种问题，通过前后端配合，使图片仅在浏览器当前视窗内出现时才加载该图片，达到减少首屏图片请求数的技术就被称为“图片懒加载”。

Picture how lazy loading technology

    在网页源码中，在img标签中首先会使用一个“伪属性”（通常使用src2，original…）去存放真正的图片链接而并非是直接存放在src属性中。当图片出现到页面的可视化区域中，会动态将伪属性替换成src属性，完成图片的加载。

Case

Crawling home owners of picture material

import scrapy
import requests
headers={
'USER_AGENT':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36'
}

class ImgzzSpider(scrapy.Spider):
    name = 'imgzz'

    start_urls = ['http://sc.chinaz.com/tupian/']

    def parse(self, response):
        src = response.xpath('//*[@id="container"]/div/div[1]/a/img/@src').extract()
        print(src) # 打印结果为空,这里的图片属性就应用的图片懒加载技术,其实图片的真正的src不是图片真正的属性
        for url in src:
            name = url.split('/')[-1]
            img = requests.get(url=url,headers=headers).content
            with open(name,'wb') as f:
                f.write(img)

analysis:

Normal visit:

Such direct write words xpath expression label positioning acquisition is empty

When the image appears to the visual area of ​​the page, the pseudo-dynamic properties will replace the src attribute, and download the image. To complete the replacement of the image properties by js

import scrapy
import requests
headers={
'USER_AGENT':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36'
}

class ImgzzSpider(scrapy.Spider):
    name = 'imgzz'

    start_urls = ['http://sc.chinaz.com/tupian/']

    def parse(self, response):
        src = response.xpath('//*[@id="container"]/div/div[1]/a/img/@src2').extract() #改为图片的真正属性
        print(src) 
        for url in src:
            name = url.split('/')[-1]
            img = requests.get(url=url,headers=headers).content
            with open(name,'wb') as f:
                f.write(img)