scrapy.Request 无法进入 callback

Question

scrapy.Request 无法进入 callback
代码如下：

    def isIdentifyingCode(self, response):
        '''判断是否存在验证码'''
        #出来代码
       pass

    def get_identifying_code(self, headers):
        # 判断页面是否需要填写验证码
        # 如果需要填写则弹出验证码，进行手动填写
        return scrapy.Request(
            url='https://www.zhihu.com/api/v3/oauth/captcha?lang=en',
            headers=header,
            callback=self.isIdentifyingCode,
            dont_filter=True)