docs: def _get_mirror_urls(self, mirrors=None, main_mirror_url=None):
          """Retrieves a list of URLs from the main mirror DNS entry
          unless a list of mirror URLs are passed.
          """
          if not mirrors:
              mirrors = get_mirrors(main_mirror_url)
              # Should this be made "less random"? E.g. netselect like?
              random.shuffle(mirrors)
  
          mirror_urls = set()
          for mirror_url in mirrors:
              # Make sure we have a valid URL
              if not ("http://" or "https://" or "file://") in mirror_url:
                  mirror_url = "http://%s" % mirror_url
              if not mirror_url.endswith("/simple"):
                  mirror_url = "%s/simple/" % mirror_url
              mirror_urls.add(mirror_url)
  
          return list(mirror_urls)