Hey all, We pass around python dataclass-based objects for our flyte task inputs and outputs, but I've noticed if I try to use a

typing.Union

type for a field, e.g.

my_param: Union[int,list[int]]=field(default_factory=list)

, Flyte complains like so:

# "Failed to extract schema for object <class 'plaster.run.sim_v3.sim_v3_params.SimV3Params'>, (will run schemaless) error: unsupported field type <fields._UnionField(dump_default=<class 'list'>, attribute=None, validate=None, required=False, load_only=False, dump_only=False, load_default=<marshmallow.missing>, allow_none=False, error_messages={'required': 'Missing data for required field.', 'null': 'Field may not be null.', 'validator_failed': 'Invalid value.'})>If you have postponed annotations turned on (PEP 563) turn it off please. Postponedevaluation doesn't work with json dataclasses"

I am not using postponed annotations in this case. The reason for my use of Union is trying to migrate the schema of a dataclass member from int to list[int]. I need to support loading older jobs, so thought the Union was an expedient solution, allowing me to init the dataclass with either an int (older jobs) or a list[int] (new jobs). I am on python 3.9 - I mention this because I seem to recall reading something related (maybe this issue?) that goes away beyond 3.9, but maybe I'm thinking of the "futures" issue related to postponed evaluations. Thanks! Thomas

you can’t use union type in dataclass for now. we are working on new dataclass transformer that allows you to serialize union

OK, thanks!