Empty .json file

你应该将

print

yield

import scrapyclass HackerItem(scrapy.Item): #declaring the item    hackertitle = scrapy.Field()class HackerSpider(scrapy.Spider):    name = 'hackernewscrawler'    allowed_domains = ['news.ycombinator.com'] # website we chose    start_urls = ['http://news.ycombinator.com/']    def parse(self,response):        sel = scrapy.Selector(response) #selector to help us extract the titles        item=HackerItem() #the item declared up# xpath of the titles        item['hackertitle'] = sel.xpath("//tr[@]/td[3]/a[@href]/text()").extract()# return items        yield item

然后运行：

scrapy crawl hackernewscrawler -o hntitles.json -t json