code: def repo_exists(self, auth, username, repo_name):
          
          path = "/repos/{u}/{r}".format(u=username, r=repo_name)
          return self._get(path, auth=auth).ok
docs: Returns whether a repository with name ``repo_name`` owned by the user with username ``username`` exists.
  
          :param auth.Authentication auth: authentication object
          :param str username: username of owner of repository
          :param str repo_name: name of repository
          :return: whether the repository exists
          :rtype: bool
          :raises NetworkFailure: if there is an error communicating with the server
          :raises ApiFailure: if the request cannot be serviced