到目前为止，我的蜘蛛代码一直运行得很好，但现在当我尝试运行一批这些蜘蛛时，所有的东西都正常工作，只是有些蜘蛛，scrapy下载了图像，其余的什么都没有。除了start_urls之外，所有的蜘蛛都是相同的。感谢任何帮助！

这是我的管道

from scrapy.contrib.pipeline.images import ImagesPipeline
from scrapy.exceptions import DropItem
from scrapy.http import Request

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

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

        for nlabel in item['nlabel']:
        yield Request(nlabel)

        print item['image_urls']


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

settings.py：

BOT_NAME = 'dmoz2'
BOT_VERSION = '1.0'

SPIDER_MODULES = ['dmoz2.spiders']
NEWSPIDER_MODULE = 'dmoz2.spiders'
DEFAULT_ITEM_CLASS = 'dmoz2.items.DmozItem'
ITEM_PIPELINES = ['dmoz2.pipelines.MyImagesPipeline']
IMAGES_STORE = '/ps/dmoz2/images'
IMAGES_THUMBS = {
#letting height be variable
#'small': ('', 120),
'small': (120, ''),
#'big': ('', 240),
'big': (300, ''),
}


USER_AGENT = '%s/%s' % (BOT_NAME, BOT_VERSION)

items.py：

from scrapy.item import Item, Field
from scrapy.utils.python import unicode_to_str

def u_to_str(text):
   unicode_to_str(text,'latin-1','ignore')


class DmozItem(Item):
   category_ids = Field()
   ....
   image_urls = Field()
   image_paths = Field()

   pass

myspider.py：

from scrapy.spider import BaseSpider
from scrapy.spider import Spider
from scrapy.selector import HtmlXPathSelector
from scrapy import Selector
from scrapy.utils.url import urljoin_rfc
from scrapy.utils.response import get_base_url
from dmoz2.items import DmozItem

class DmozSpider(Spider):
   name = "fritos_jun2015"
   allowed_domains = ["walmart.com"]
   start_urls = [

    "http://www.walmart.com/ip/Fritos-Bar-B-Q-Flavored-Corn-Chips-9.75- oz/36915853",
    "http://www.walmart.com/ip/Fritos-Corn-Chips-1-oz-6-count/10900088",

]


def parse(self, response):
    hxs = Selector(response)
    sites = hxs.xpath('/html/body/div[1]/section/section[4]/div[2]')
    items = []
    for site in sites:
        item = DmozItem()
        item['category_ids'] = ''
        .....
        item['image_urls'] = site.xpath('div[1]/div[3]/div[1]/div/div/div[2]/div/div/div[1]/div/div/img[2]/@src').extract()
        items.append(item)
    return items

我真的很想知道为什么这只蜘蛛有时会抓取图像，而有时却不抓取图像。除了来自同一个allowed_domain的start_url之外，所有的蜘蛛都是相同的。而且图像都是绝对路径，路径是正确的。

提前道谢。-TM