How to use the fastavro.io.symbols.String function in fastavro

"name",
                            candidate_schema.get("type")
                        )
                    )
                else:
                    labels.append(candidate_schema)

            return Sequence(Alternative(symbols, labels), Union())

        elif record_type == "map":
            repeat = Repeater(
                MapEnd(),
                # ItemEnd(),  # TODO: Maybe need this?
                self._parse(schema["values"]),
                MapKeyMarker(),
                String(),
            )
            return Sequence(repeat, MapStart())

        elif record_type == "array":
            repeat = Repeater(
                ArrayEnd(),
                ItemEnd(),
                self._parse(schema["items"]),
            )
            return Sequence(repeat, ArrayStart())

        elif record_type == "enum":
            return Sequence(EnumLabels(schema["symbols"]), Enum())

        elif record_type == "null":
            return Null()

def write_utf8(self, value):
        self._parser.advance(String())
        if self._parser.stack[-1] == MapKeyMarker():
            self._parser.advance(MapKeyMarker())
            self.write_object_key(value)
        else:
            self.write_value(value)

repeat = Repeater(
                ArrayEnd(),
                ItemEnd(),
                self._parse(schema["items"]),
            )
            return Sequence(repeat, ArrayStart())

        elif record_type == "enum":
            return Sequence(EnumLabels(schema["symbols"]), Enum())

        elif record_type == "null":
            return Null()
        elif record_type == "boolean":
            return Boolean()
        elif record_type == "string":
            return String()
        elif record_type == "bytes":
            return Bytes()
        elif record_type == "int":
            return Int()
        elif record_type == "long":
            return Long()
        elif record_type == "float":
            return Float()
        elif record_type == "double":
            return Double()
        elif record_type == "fixed":
            return Fixed()
        else:
            raise Exception("Unhandled type: {}".format(record_type))

def read_utf8(self):
        self._parser.advance(String())
        if self._parser.stack[-1] == MapKeyMarker():
            self._parser.advance(MapKeyMarker())
            for key in self._current:
                self._key = key
                break
            return self._key
        else:
            return self.read_value()