我在middlewares.py > process_request中有以下代码：

def process_request(self, request, spider):
        refreerr_list = [
            'https://google.com',
            'https://amazon.com',
            'https://facebook.com',.....
        ]
        referr = random.choice(refreerr_list)

        request.header['referer'] = referr

因为它应该显示referer，但在日志中，它显示：

2022-07-17 07:17:13 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://www.amazon.com/AMD-Ryze.....RO-3995WX/dp/B08V5HPXVY> (referer: None)

我是否必须在www.example.com中添加一些内容settings.py?
但在settings.py中执行以下操作时，它有效：

DEFAULT_REQUEST_HEADERS = {
  'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',,
  'referer': 'https://www.amazon.com/',
}

感谢您的帮助！