(8)分布式下的爬虫Scrapy应该如何做-图片下载(源码放送)

转载主注明出处：http://www.cnblogs.com/codefish/p/4968260.html

在爬虫中，我们遇到比较多需求就是文件下载以及图片下载，在其它的语言或者框架中，我们可能在经过数据筛选，然后异步的使用文件下载类来达到目的，Scrapy框架中本身已经实现了文件及图片下载的文件，相当的方便，只要几行代码，就可以轻松的搞定下载。下面我将演示如何使用scrapy下载豆瓣的相册首页内容。

优点介绍：

1)自动去重

2)异步操作，不会阻塞

3)可以生成指定尺寸的缩略图

4)计算过期时间

5)格式转化

编码过程：

一，定义Item

# -*- coding: utf-8 -*-

# Define here the models for your scraped items
#
# See documentation in:
# http://doc.scrapy.org/en/latest/topics/items.html

import scrapy
from scrapy import Item,Field



class DoubanImgsItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    image_urls = Field()
    images = Field()
    image_paths = Field()
    pass

二，定义spider

#coding=utf-8
from scrapy.spiders import Spider
import re
from douban_imgs.items import DoubanImgsItem
from scrapy.http.request import Request
# please pay attention to the encoding of info,otherwise raise error
import sys
reload(sys)
sys.setdefaultencoding('utf8')


class download_douban(Spider):
    name = 'download_douban'
    def __init__(self, url='152686895', *args, **kwargs):
        self.allowed_domains = ['douban.com']
        self.start_urls = [
                'http://www.douban.com/photos/album/%s/' %(url) ]
        #call the father base function
        self.url = url
        super(download_douban, self).__init__(*args, **kwargs)

    def parse(self, response):
        """
        :type response: response infomation
        """
        list_imgs = response.xpath('//div[@class="photolst clearfix"]//img/@src').extract()
        if list_imgs:
            item = DoubanImgsItem()
            item['image_urls'] = list_imgs
            yield item

三，定义piepline

# -*- coding: utf-8 -*-

# Define your item pipelines here
#
# Don't forget to add your pipeline to the ITEM_PIPELINES setting
# See: http://doc.scrapy.org/en/latest/topics/item-pipeline.html
from scrapy.pipelines.images import ImagesPipeline
from scrapy.exceptions import DropItem
from scrapy import Request
from scrapy import log



class DoubanImgsPipeline(object):
    def process_item(self, item, spider):
        return item



class DoubanImgDownloadPieline(ImagesPipeline):
    def get_media_requests(self,item,info):
        for image_url in item['image_urls']:

            yield Request(image_url)

    def item_completed(self, results, item, info):
        image_paths = [x['path'] for ok, x in results if ok]
        if not image_paths:
            raise DropItem("Item contains no images")
        item['image_paths'] = image_paths
        return item

四，定义setting.py，启用item处理器

# Configure item pipelines
# See http://scrapy.readthedocs.org/en/latest/topics/item-pipeline.html
ITEM_PIPELINES = {
   'douban_imgs.pipelines.DoubanImgDownloadPieline': 300,
}


IMAGES_STORE='C:\\doubanimgs'

IMAGES_EXPIRES = 90