docs: def compare(self, base, head):
          """
          :calls: `GET /repos/:owner/:repo/compare/:base...:head <http://developer.github.com/v3/repos/commits>`_
          :param base: string
          :param head: string
          :rtype: :class:`github.Comparison.Comparison`
          """
          assert isinstance(base, (str, unicode)), base
          assert isinstance(head, (str, unicode)), head
          headers, data = self._requester.requestJsonAndCheck(
              "GET",
              self.url + "/compare/" + base + "..." + head
          )
          return github.Comparison.Comparison(self._requester, headers, data, completed=True)