def parse(self, response): ? ?post_nodes = response.css('.search_txt h3 a') ? ?for post_url in post_nodes.css("::attr(href)").extract_first(""): ? ? ? ?post_url=parse.urljoin(response.url, post_url) ? ? ? ?yield Request(url=post_url,callback=self.parse_item)我這段代碼為啥回調(diào)不到parse_item