python - Scrapy空白断言错误？

Question

下面的代码对于发送到解析方法的每个请求都会抛出以下错误(Scrapy v0.24.4):

2014-12-30 01:20:06+0000 [yelp_spider] DEBUG: Crawled (200) <GET http://www.yelp.com/biz/lookout-tavern-oak-bluffs> (referer: http://www.yelp.com/search?find_desc=Restaurants&find_loc=02557&ns=1) ['partial']
2014-12-30 01:20:06+0000 [yelp_spider] ERROR: Spider error processing <GET http://www.yelp.com/biz/lookout-tavern-oak-bluffs>
        Traceback (most recent call last):
          File "/usr/lib/python2.7/site-packages/scrapy/core/scraper.py", line 111, in _scrape_next
            self._scrape(response, request, spider).chainDeferred(deferred)
          File "/usr/lib/python2.7/site-packages/scrapy/core/scraper.py", line 118, in _scrape
            dfd = self._scrape2(response, request, spider) # returns spiders processed output
          File "/usr/lib/python2.7/site-packages/scrapy/core/scraper.py", line 128, in _scrape2
            request_result, request, spider)
          File "/usr/lib/python2.7/site-packages/scrapy/core/spidermw.py", line 69, in scrape_response
            dfd = mustbe_deferred(process_spider_input, response)
        --- <exception caught here> ---
          File "/usr/lib/python2.7/site-packages/scrapy/utils/defer.py", line 39, in mustbe_deferred
            result = f(*args, **kw)
          File "/usr/lib/python2.7/site-packages/scrapy/core/spidermw.py", line 48, in process_spider_input
            return scrape_func(response, request, spider)
          File "/usr/lib/python2.7/site-packages/scrapy/core/scraper.py", line 138, in call_spider
            dfd.addCallbacks(request.callback or spider.parse, request.errback)
          File "/usr/lib64/python2.7/site-packages/twisted/internet/defer.py", line 288, in addCallbacks
            assert callable(callback)
        exceptions.AssertionError:

代码:

import scrapy
from scrapy import Request
import re

ROOT_URL = "http://www.yelp.com"

class YelpReview(scrapy.Item):
    zip_code = scrapy.Field()
    review_date = scrapy.Field()

class yelp_spider(scrapy.Spider):
    name = 'yelp_spider'
    allowed_domains = ['yelp.com']
    start_urls = ["http://www.yelp.com/search?find_desc=Restaurants&find_loc=02557&ns=1"]

    def parse(self, response):
        business_urls = [business_url.extract() for
                business_url in response.xpath('//a[@class="biz-name"]/@href')[1:]
                ]
        for business_url in business_urls:
            yield Request(url=ROOT_URL + business_url, callback="scrape_reviews")

        if response.url.find('?start=') == -1:
            self.createRestaurantPageLinks(response)

    def scrape_reviews(self, response):
        reviews = response.xpath('//meta[@itemprop="datePublished"]/@content')
        item = YelpReview()

        for review in reviews:
            item['zip_code'] = "02557"
            item['review_date'] = review.extract()
            yield item

        if response.url.find('?start=') == -1:
            self.createReviewPageLinks(response)

    def createRestaurantPageLinks(self, response):
        raw_num_results = response.xpath('//span[@class="pagination-results-window"]/text()').extract()[0]
        num_business_results = int(re.findall(" of (\d+)", raw_num_results)[0])
        BUSINESSES_PER_PAGE = 10
        restaurant_page_links = [Request(url=response.url + '?start=' + str(BUSINESSES_PER_PAGE*(n+1)),
            callback="parse") for n in range(num_business_results/BUSINESSES_PER_PAGE)]

        return restaurant_page_links

    def createReviewsPageLinks(self, response):
        REVIEWS_PER_PAGE = 40
        num_review_results = int(response.xpath('//span[@itemprop="reviewCount"]/text()').extract()[0])
        review_page_links = [Request(url=response.url + '?start=' + str(REVIEWS_PER_PAGE*(n+1)),
            callback="scrape_reviews") for n in range(num_review_results/REVIEWS_PER_PAGE)]

        return review_page_links

我尝试进行了一系列更改，但仍然无法弄清楚是什么触发了此错误。

Answer 1

您需要从 parse() 方法返回:

if response.url.find('?start=') == -1:
    return self.createRestaurantPageLinks(response)