class ModelWithCustomEncoder(BaseModel):
        dt_field: datetime

        @field_serializer("dt_field")
        def serialize_dt_field(self, dt):
            return dt.replace(microsecond=0, tzinfo=timezone.utc).isoformat()

    class ModelWithCustomEncoderSubclass(ModelWithCustomEncoder):
        pass

    model = ModelWithCustomEncoder(dt_field=datetime(2019, 1, 1, 8))

        date_part = match.group(2)

        if date_part:
            print(f"Latest release {version} already has a date: {date_part}")
            sys.exit(0)

        today = date.today().isoformat()
        lines[i] = f"## {version} ({today})\n"
        print(f"Added date: {version} ({today})")

        with open(RELEASE_NOTES_FILE, "w") as f:
            f.writelines(lines)
        sys.exit(0)

                secret_key=creds.get_child_text('SecretAccessKey'),
                token=creds.get_child_text('SessionToken'),
                expiry_time=parse(creds.get_child_text('Expiration')).isoformat())

            "date": datetime(2021, 7, 26).isoformat(),
            "price": None,
            "owner_ids": None,
        },
        {
            "name": "bar",
            "date": datetime(2021, 7, 26).isoformat(),
            "price": 1.0,
            "owner_ids": None,
        },
        {
            "name": "baz",
            "date": datetime(2021, 7, 26).isoformat(),
            "price": 2.0,

        dt_field: datetime

        @field_serializer("dt_field")
        def serialize_datetime(self, dt_field: datetime):
            return dt_field.replace(microsecond=0, tzinfo=timezone.utc).isoformat()

    app = FastAPI()
    model = ModelWithDatetimeField(dt_field=datetime(2019, 1, 1, 8))

    @app.get("/model", response_model=ModelWithDatetimeField)
    def get_model():
        return model