Implements the call() function with same signature as Client.call().  Raises
        a RpcException if send() has already been called on this batch.  Otherwise
        appends the request to an internal list.

        This method is not commonly called directly.

def call(self, iface_name, func_name, params):
        """
        Implements the call() function with same signature as Client.call().  Raises
        a RpcException if send() has already been called on this batch.  Otherwise
        appends the request to an internal list.

        This method is not commonly called directly.
        """
        if self.sent:
            raise Exception("Batch already sent. Cannot add more calls.")
        else:
            req = self.client.to_request(iface_name, func_name, params)
            self.req_list.append(req)