How to use the nfstream.classifier.NFStreamClassifier.on_flow_update function in nfstream

def on_flow_update(self, packet_information, flow, direction):
        NFStreamClassifier.on_flow_update(self, packet_information, flow, direction)
        if flow.classifiers[self.name]['detection_completed'] == 0:  # process till not completed
            flow.classifiers[self.name]['detected_protocol'] = ndpi.ndpi_detection_process_packet(
                self.mod,
                byref(flow.classifiers[self.name]['ndpi_flow']),
                cast(cast(c_char_p(packet_information.raw), c_void_p), POINTER(c_uint8)),
                len(packet_information.raw),
                int(packet_information.timestamp),
                flow.classifiers[self.name]['src_id'],
                flow.classifiers[self.name]['dst_id']
            )

            enough_packets = ((flow.ip_protocol == 6) and ((flow.src_to_dst_pkts + flow.dst_to_src_pkts) >
                                                           self.max_num_tcp_dissected_pkts)) or \
                             ((flow.ip_protocol == 17) and ((flow.src_to_dst_pkts + flow.dst_to_src_pkts) >
                                                            self.max_num_udp_dissected_pkts))