Is there a Prefect 2 equivalent to doing

raise SKIP("not applicable")

in order to skip a task? If I just

return Cancelled(message="not applicable")

instead of returning my task’s actual data, will that have the same effect?

I believe

Cancelled

has the functionality you are looking for! From the docs: "The run did not complete because a user determined that it should not." https://docs.prefect.io/concepts/states/?h=states#state-types

Sorry, I wasn’t clear enough there. I get that I want the

Cancelled

state, my confusion is that in Prefect 1 I would

raise

a state as an exception in order to set the task run to that state. In Prefect 2 can I

return

a state to do the same thing?

Yep! You can manually return a state, there's some examples here: https://docs.prefect.io/concepts/flows/?h=state#return-a-manual-state

Those docs show returning a state in flows, it’s not obvious from them whether the same thing can be done in tasks

Hi Eli, you can totally return states, check out the draft of this blog post (not released yet but might be already helpful to you) https://medium.com/p/5eaabdfbb70e#bac0-f33b95e8f816

We also discovered a bug when raising the

Cancelled

state that you can follow here: https://github.com/PrefectHQ/prefect/issues/6789 Thanks for helping us find this bug!! A work around for this could be to return the

Completed

state with the correct message just like in the example above.

Thanks Anna, I ’ve just ended up doing something like this

@task
def lambda(request):
    # invoke lambda here, parse respoonse to `payload`
    if payload.not_applicable:
        return Cancelled("not applicable")
    return payload.calculated

@flow
def flow():
    requests = generate_requests()
    for request in requests:
        fut = lambda.submit(request)
        if fut.wait().is_completed():
            save_to_postgres.submit(fut.result())

but my flow runs were still marked as failed. It looks like

Cancelled

is treated as a failed state for the purposes of determining whether a flow failed overall, which the docs don’t mention! I’ll try the

None

-returning method you suggested

Great point Eli and well done! The docs mention here https://docs.prefect.io/concepts/states/ that the Cancelled state indicates "The run did not complete because a user determined that it should not." - it's essentially interrupting and failing the run early because you determined that it should not continue -- but I understand what you mean, in Prefect 1.0 Cancelled was marked in the UI as grey to indicate it's neither success, nor failure

yep, totally understand the difficulty, I’ve just got a lot of Prefect 1 to unlearn! Returning

None

from the task and checking it in the flow with

for request in requests:
    output = lambda(request)
    if output.result() is not None:
        save_to_postgres(output)

seems to have worked great. Thanks for all your help!