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

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_fixed(self, size):
        self._parser.advance(Fixed())
        return utob(self.read_value(), encoding='iso-8859-1')

def write_fixed(self, value):
        self._parser.advance(Fixed())
        self.write_value(btou(value, encoding='iso-8859-1'))