    async def start(self):
        """Start the single-user server

        Returns:
          (str, int): the (ip, port) where the Hub can connect to the server.

        .. versionchanged:: 0.7
            Return ip, port instead of setting on self.user.server directly.
        """
        raise NotImplementedError("Override in subclass. Must be a coroutine.")
Start the single-user server

Returns:
(str, int): the (ip, port) where the Hub can connect to the server.

.. versionchanged:: 0.7
Return ip, port instead of setting on self.user.server directly.
jupyterhub/spawner.py