How to use the choochoo.fit.decode.Definition function in choochoo

def __add_definition(self, local_type, extended):
        endian = self.__data[self.__offset+2] & 0x1
        global_type = unpack('<>'[endian]+'H', self.__data[self.__offset+3:self.__offset+5])[0]
        message = self.__messages.number_to_message(global_type)
        identity = Identity(message.name, self.__defn_counter)
        n_fields = self.__data[self.__offset+5]
        fields = tuple(self.__fields(self.__field,self.__offset+6, n_fields, message))
        offset = 6 + n_fields * 3
        if extended:
            n_dev_fields = self.__data[self.__offset+offset]
            dev_fields = tuple(self.__fields(self.__dev_field, self.__offset+offset+1, n_dev_fields))
            offset += 1 + n_dev_fields * 3
        else:
            dev_fields = ()
        self.__definitions[local_type] = Definition(self.__log, identity, endian, message, fields, dev_fields)
        return offset