Hello. In Prefect2, I have a flow with

**kwargs

for its input parameter like

my_flow (p_1, p_2, **kwargs:dict[str, bool])

. When I run the flow from the UI, I get

Validation of flow parameters failed with error: 
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/prefect/engine.py", line 296, in retrieve_flow_then_begin_flow_run
    parameters = flow.validate_parameters(flow_run.parameters)
  File "/usr/local/lib/python3.9/site-packages/prefect/flows.py", line 339, in validate_parameters
    raise ParameterTypeError.from_validation_error(exc) from None
prefect.exceptions.ParameterTypeError: Flow run received invalid parameters:
 - kwargs: value is not a valid dict

the parameter value is:

{
  "kwargs": {
    "p_1": false
  }
}

Am I doing something wrong, or is this a bug in validate_parameters? Thank you

hi @Mansour Zayer - can you share how you actually defined your flow's signature (just the whole flow definition if possible)?

I want to provide the skip arguments from the parallel_orchestrator using **kwargs.

@flow
async def my_subflow(
    input_1: str,
    skip_step_1: bool = False,
    skip_step_2: bool = False,
    skip_step_3: bool = False,
    **kwargs: dict,
    ):
    doing_something

@flow
async def parallel_orchestrator(skip_step: bool = False, list_of_input=["a", "b", "c", "d"], **kwargs:dict[str, bool]):
    some steps here
    await asyncio.gather(
            *[
                run_deployment(
                    name=f"my-subflow/...",
                    parameters=dict(input_1=input, **kwargs),
                )
                for input in list_of_input
            ]
        )

can you show how you're passing in your parameter value? I imagine pydantic is unable to parse what you passed in as a

dict[str, bool]

also just as a side note, I would generally recommend avoiding mutable defaults (like

list_of_input

) for your flow parameters (this is an aggressively worded article 😅 but gets the point across)

I experimented with different type hints (

dict

,

dict[str, bool]

,

Optional[dict]

), nothing worked.

hmm. i wonder if you actually need to use

**kwargs

here, it feels like it may be simpler and more explicit if you replace it with something like

static_kwargs: Dict[str, Any]

(not using

**

) and just pass each instance of

my_subflow

that dictionary - or is there a reason you can't do that?

This is the input to the parallel orchestrator which causes failure as invalid dict. Thanks for your help Nate. I'll go with the static_kwargs. I tested it and it achieves my goal.

ahh I see, sounds good!

I’m not sure if this is an issue with validation, but when you add a type annotation for

kwargs

you are actually specifying the type for each keyword argument

Thanks for the good point Zanie. Prefect UI treats

**kwargs

like a regular parameter. For example, it's treated as mandatory, but you can't define default values for

**kwargs

. Also, any type hint you use, the UI will try to cast the

kwargs

value to that type. Therefore, I think this article doesn't apply 100% here.