How to use the qi.future.Future function in qi

def listen(self, address, async=False):
        """Listen on given address.

        :param address: A valid IPv4 address we can bind to.
        """
        fut = Future(_qipy.qi_session_listen(self._session, address))
        if async:
            return fut
        if fut.has_error():
            #todo: another error?
            raise ConnectionError('Cannot listen on ' + address + ': ' + fut.error())

def services(self, async=False):
        """Retrieves the list of the names of all the services available on the
        service directory."""
        fut = Future(_qipy.qi_session_get_services(self._session))
        if async:
            return fut
        return fut.value()

def connect(self, address, async=False):
        """ Connect to service directory.

        :raises: ConnectionError
        """

        fut = Future(_qipy.qi_session_connect(self._session, address))
        if async:
            return fut
        if fut.has_error():
            raise ConnectionError('Cannot connect to ' + address + ': ' + fut.error())

def register_service(self, name, obj, async=False):
        """Register given service and expose it to the world.

        :param name: Name of the service to register.
        :param obj: The actual service to bind.
        :returns: The id of the service.
        """
        #TODO
        fut = Future(_qipy.qi_session_register_service(self._session, name, obj._obj))
        if async:
            return fut
        return fut.value()

def unregister_service(self, idx, async=False):
        """Unregister service, it is not visible anymore.

        :param idx: id of the service given on register.
        """
        #TODO
        fut = Future(_qipy.qi_session_unregister_service(self._session, idx))
        if async:
            return fut
        return fut.value()

def service(self, name, default=None, async=False):
        """Fetches a new instance of GenericObject binding to a service. If the
        service is unknown, returns *default*.

        :param name: Name of the service.
        :param default: Default value if service is unknown.
        """
        if not isinstance(name, str):
            raise TypeError('keys must be strings.')

        # Get C object.
        fut = Future(_qipy.qi_session_get_service(self._session, name))
        if async:
            return fut
        return fut.value()