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howdy id like to have an action in my tasks/flows happen upon cancellation from the prefect ui - is ...
# ask-community
a
howdy id like to have an action in my tasks/flows happen upon cancellation from the prefect ui - is this doable?
k
Hi @Andrew Nichol! Have you checked out the Automations tab in the UI?
a
hmm looks like that could be helpful but id like the state conditions and actions all to be defined in code
k
Let me check with the team if a terminal state handler will still run upon flow cancelletation
You can’t do it on the task level but you can do it with the state handler and check for the cancelled state
a
that looks like it should work - will test and return. thanks @Kevin Kho!
so it appears that using state_handlers at the flow level works for this whereas at the task level it does not
however upon cancellation i want the flow to do something based on some variables which can be found inside of tasks
the easiest way i found to do this is with global variables
ideally i could avoid that but for now it works
here is some example code
Copy code
def run_on_cancel(task, old_state, new_state):
    global some_global_variable
    if isinstance(new_state, prefect_state.Cancelled):
        logger = prefect_context.get("logger")
        <http://logger.info|logger.info>(F"Running CANCELATION: {some_global_variable}")
        raise Exception(f"exiting because of Cancelled state: {some_global_variable}")
    return new_state

@task
def supposed_to_succeed():
    global some_global_variable
    some_global_variable = "beaver"
    logger = prefect_context.get("logger")
    <http://logger.info|logger.info>("Running success")
    sleep(15)
    return True

with Flow(
    "failure-flow",
    executor=LocalDaskExecutor(),
    result=PrefectResult(),
    state_handlers=[run_on_cancel]
) as failure_flow:
    some_global_variable = None
    succeed = supposed_to_succeed()
    maybe_failure = supposed_to_fail(succeed)
    last(maybe_failure)
k
This is right. You can’t do this on a task level unfortunately and there’s no way for the state handler to be able to get variables from the task other than the way you did I think. (First time I’ve seen it actually!)
a
okay thanks much for your help
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