code: def compare_commits(self, base, head):
          
          url = self._build_url('compare', base + '...' + head,
                                base_url=self._api)
          json = self._json(self._get(url), 200)
          return Comparison(json) if json else None
docs: Compare two commits.
  
          :param str base: (required), base for the comparison
          :param str head: (required), compare this against base
          :returns: :class:`Comparison <github3.repos.comparison.Comparison>` if
              successful, else None