Python 脏兮兮的空白断言错误？

下面的代码针对发送到解析方法（Scrapy v0.24.4）的每个请求抛出以下错误：

---

我已尝试进行了大量更改，但仍然无法找出触发此错误的原因。

您需要从

parse（）

方法返回：

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

---

这个

callback=“scrape_reviews”

不应该是

callback=self.scrape_reviews

？这样，我得到了错误：SyntaxError:'return'和生成器中的参数

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

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