Add the specified users or groups to this project role.

        One of ``users`` or ``groups`` must be specified.

        :param users: a user or users to add to the role
        :type users: string, list or tuple
        :param groups: a group or groups to add to the role
        :type groups: string, list or tuple

def add_user(self, users=None, groups=None):
        """Add the specified users or groups to this project role.

        One of ``users`` or ``groups`` must be specified.

        :param users: a user or users to add to the role
        :type users: string, list or tuple
        :param groups: a group or groups to add to the role
        :type groups: string, list or tuple
        """

        if users is not None and isinstance(users, string_types):
            users = (users,)
        if groups is not None and isinstance(groups, string_types):
            groups = (groups,)

        data = {
            'user': users}
        self._session.post(self.self, data=json.dumps(data))