问如何在Scrapy的"yield“中设置异常？

EN

rules = [
    Rule(LinkExtractor(allow=('Repositories'), restrict_xpaths=('//a[@rel="next"]'))),
    Rule(LinkExtractor(allow=('github'), restrict_xpaths=('//h3/a[@class="v-align-middle"]')), callback='parse_project'),
    Rule(LinkExtractor(allow=('commits/master'), restrict_xpaths=('//*[@class="commits"]/a')), follow=True, callback='parse_commits_page'),
    Rule(LinkExtractor(deny=('\+174'), restrict_xpaths=('//a[contains(text(), "Older")]')), follow=True, callback='parse_commits_page')
]

# Parse the main page of the project
def parse_project(self, response):
    yield {
        'author': response.xpath('//a[@rel="author"]/text()').extract(),
        'name': response.xpath('//strong[@itemprop="name"]/a/text()').extract(),
        'tags': [x.strip() for x in response.xpath('//a[contains(@class, "topic-tag")]/text()').extract()],
        'about': response.xpath('//*[@itemprop="about"]/text()').extract_first().strip(),
        'lang_name': response.xpath('//span[@class = "lang"]/text()').extract(),
        'lang_perc' : response.xpath('//span[@class = "percent"]/text()').extract(),
        'stars': response.xpath('//a[contains(@aria-label, "starred")]/text()').extract_first().strip(),
        'forks': response.xpath('//a[contains(@aria-label, "forked")]/text()').extract_first().strip(),
        'commits': response.xpath('//a[contains(., "commits")]/span/text()').extract_first().strip(),
        'contributors': response.xpath('//a[contains(., "contributor")]/span/text()').extract_first().strip(),
        'last_commits': None
    }

def pre_parse_project(self, response):
    yield scrapy_splash.SplashRequest(response.url, self.parse_project,
        args={
            'wait': 4,
        }
    )