def user_exists(self, username):
        """
        Returns whether a user with username ``username`` exists.

        :param str username: username of user
        :return: whether a user with the specified username exists
        :rtype: bool
        :raises NetworkFailure: if there is an error communicating with the server
        :return:
        """
        path = "/users/{}".format(username)
        return self._get(path).ok