'Check a request-provided group model from a REST API'

def _check_group_model(self, model):

    self._check_model(model, self._group_model_types, 'group')
    for groupname in model.get('groups', []):
        if (not isinstance(groupname, str)):
            raise web.HTTPError(400, ('group    names    must    be    str,    not    %r', type(groupname)))
