docs: def get_archive_link(self, archive_format, ref=github.GithubObject.NotSet):
          """
          :calls: `GET /repos/:owner/:repo/:archive_format/:ref <http://developer.github.com/v3/repos/contents>`_
          :param archive_format: string
          :param ref: string
          :rtype: string
          """
          assert isinstance(archive_format, (str, unicode)), archive_format
          assert ref is github.GithubObject.NotSet or isinstance(ref, (str, unicode)), ref
          url = self.url + "/" + archive_format
          if ref is not github.GithubObject.NotSet:
              url += "/" + ref
          headers, data = self._requester.requestJsonAndCheck(
              "GET",
              url
          )
          return headers["location"]