如何让Python Scrapy从网页中提取所有外部链接的所有域？

import scrapy
from scrapy.linkextractors import LinkExtractor
from urllib.parse import urlparse

class MySpider(scrapy.Spider):
    name = 'my_spider'
    start_urls = ['http://example.com']
    allowed_domains = ['example.com']

    def parse(self, response):
        # 提取所有外部链接
        link_extractor = LinkExtractor(allow_domains=self.allowed_domains, unique=True)
        links = link_extractor.extract_links(response)

        # 提取链接的域名
        domains = set()
        for link in links:
            parsed_url = urlparse(link.url)
            domain = parsed_url.netloc
            domains.add(domain)

        # 打印所有域名
        for domain in domains:
            print(domain)

scrapy crawl my_spider