    def _usernames_to_users(self, usernames):
        """Turn a list of usernames into user objects"""
        users = []
        for username in usernames:
            username = self.authenticator.normalize_username(username)
            user = self.find_user(username)
            if user is None:
                raise web.HTTPError(400, f"No such user: {username}")
            users.append(user.orm_user)
        return users
Turn a list of usernames into user objects
jupyterhub/apihandlers/groups.py