How to use the netflow.ipfix.IPFIXFieldTypes.by_id function in netflow

self.fields = set()
        offset = 0
        unpacker = "!"
        discovered_fields = []

        # Iterate through all fields of this template and build the unpack format string
        # See https://www.iana.org/assignments/ipfix/ipfix.xhtml
        for index, field in enumerate(template):
            field_type_id = field.id
            field_length = field.length
            offset += field_length

            # Here, reduced-size encoding of fields blocks the usage of IPFIXFieldTypes.get_type_unpack.
            # See comment in IPFIXFieldTypes.get_type_unpack for more information.

            field_type = IPFIXFieldTypes.by_id(field_type_id)  # type: Optional[FieldType]
            if not field_type and type(field) is not TemplateFieldEnterprise:
                # This should break, since the exporter seems to use a field identifier
                # which is not standardized by IANA.
                raise NotImplementedError("Field type with ID {} is not implemented".format(field_type_id))

            datatype = field_type.type  # type: str
            discovered_fields.append((field_type.name, field_type_id))

            # Catch fields which are meant to be raw bytes and skip the rest
            if IPFIXDataTypes.is_bytes(datatype):
                unpacker += "{}s".format(field_length)
                continue

            # Go into int, uint, float types
            issigned = IPFIXDataTypes.is_signed(datatype)
            isfloat = IPFIXDataTypes.is_float(datatype)

def data(self):
        return {
            IPFIXFieldTypes.by_id(key)[1]: value for (key, value) in self.fields
        }