docs: def _extract_key_info(self, request):
          """
          从欲下载资源的request中, 获得资源上传七牛时的bucket和key
          """
          from scrapy.utils.request import request_fingerprint
  
          key_generator = request.meta.get('qiniu_key_generator')
          if key_generator:
              tmp = key_generator(request.url)
              bucket = tmp['bucket'] or self.bucket
              key = tmp['key']
          else:
              bucket = self.bucket
              key = '%s%s' % (self.key_prefix, request_fingerprint(request))
  
          return {'bucket': bucket, 'key': key}