Image Pipeline

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2019-9-7

Image Pipeline

Scrapy 提供了专门下载文件或者图片的Pipeline，下载图片与文件的原理同抓取网页的原理是一样的，所以他们的下载过程支持多线程与异步，十分的高效

Image Pipeline的工作流程

itemPipeline从item中获取需要下载的数据，通过Request重新放入到项目队列等待调度器调度下载
当图片下载完成，另一个组(images)将被更新到结构中,其中包括下载图片的信息,比如下载路径,源抓取地址(从image_urls组获得)和图片的校验码. images列表中的图片顺序将和源image_urls组保持一致.如果某个图片下载失败,将会记录下错误信息,图片也不会出现在images组中

参考链接

案例

首先在settings中配置图片存放路径
```
IMAGES_STORE = './images'
```

在item中定义需要的数据结构

class Images360Item(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    collection = table = "images"
    id = scrapy.Field()
    title = scrapy.Field()
    url = scrapy.Field()
    thumb = scrapy.Field()

定义spider与parse

import scrapy
from urllib.parse import urlencode
from scrapy import Request
from images360.images360.items import Images360Item

class ImagesSpider(scrapy.Spider):
    name = 'images'
    allowed_domains = ['images.so.com']
    start_urls = ['http://images.so.com/']

    def start_requests(self):
        data = {'ch': 'photography',
                'listtype': 'hot', }
        base_url = 'http://images.so.com/zj?'
        for page in range(1, self.settings.get('MAX_PAGE_SIZE') + 1):
            sn = page * 30
            data['sn'] = sn
            params = urlencode(data)
            url = base_url + params
            print(url)
            yield Request(url, self.parse)

    def parse(self, response):
        html = json.loads(response.text)
        datas = html.get('list', '')
        if datas:
            for data in datas:
                images_item = Images360Item()
                images_item['id'] = data.get('imageid', '')
                images_item['title'] = data.get('group_title', '')
                images_item['url'] = data.get('qhimg_url', '')
                images_item['thumb'] = data.get('qhimg_thumb_url', '')
                yield images_item

定义项目管道

from scrapy import Request
from scrapy.exceptions import DropItem
from scrapy.pipelines.images import ImagesPipeline

class ImagesPipeline(ImagesPipeline):

    # 将item中的url取出来 通过Request继续放入到调度器中执行
    def get_media_requests(self, item, info):
        yield Request(item['url'])

    # request对应的是当前下载对象，该函数用于放回 文件名
    def file_path(self, request, response=None, info=None):
        url = request.url
        print('url============', url)
        file_name = url.split('/')[-1]
        return file_name

    # 单个item完成下载时的处理方法
    def item_completed(self,results,item,info):
             # results为Item对应的下载结果
        # print(results) 
        # [(True, {'url': 'http://p2.so.qhimgs1.com/t01b866193d9b2101de.jpg', 'path': 't01b866193d9b2101de.jpg',
        #          'checksum': 'e074b5cbacd22ac38480d84506fedf02'})]

        image_path = [x['path'] for ok,x in results if ok]
        if image_path:
            return item
        else:
            raise DropItem('image download failed')

注：ImagePipeline的优先级别应该比存入数据库的级别高

作者：学一点也是好

原文地址：https://www.cnblogs.com/mangM/p/10768406.html

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Image Pipeline的工作流程

案例

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