Hey guys there a reason for signals `FAIL` `PrefectStateSign

Question

Hey guys there a reason for signals `FAIL` `PrefectStateSignal` `PrefectSignal` inherit from `BaseException` instead of `Exception`

FuETL · Answer

Sorry to bump it is because i faced some issues using ```try except Exception as err pass``` and raising fail signal it was not being catched

Anna Geller · Answer

what problem are you trying to solve

Anna Geller · Answer

you don t need to use try except necessarily when you use Prefect signals were needed in v1 to do things like skipping some tasks raising a retry signal to cause a rerun of something or pausing the execution in some other way once you migrate to v2 you can use native python so signals won t be required

Anna Geller · Answer

internally in v1 we are using those signals to bypass all other exception handling since they are signals not actual errors

Anna Geller · Answer

but those shouldn t be caught unless you want to use them e g raise SKIP or RETRY signal

FuETL · Answer

< Anna Geller> Thanks for the answer i using v1 basically my usage is i have a task lets say with 3 retries If is the last retry before raise FAIL signal again i need to send a e mail to notify the interested parties so inside my task i raise SIGNAL and catch them in the `except` statement that was the cause of this question

FuETL · Answer

and of course if is last time i send the email and then raise the signal smile

Anna Geller · Answer

this post has all the info you need <https discourse prefect io t is there an equivalent to sensors in prefect how do i trigger event driven workflows 76>

Anna Geller · Answer

```import pendulum from prefect engine signals import RETRY import awswrangler as wr def check if file arrived in s3 return wr s3 does object exist <s3 bucket example file csv> task def s3 sensor kwargs bool s3 object arrived = check if file arrived in s3 if bool s3 object arrived is False raise RETRY File not available yet retrying in 20 seconds start time=pendulum now add seconds=20 ```