Does anyone have a working example of specifying a `result h

Question

Does anyone have a working example of specifying a `result handler` and having `write ` amp `read ` functions called Mainly interested in `result handler` on a Task but Flow level or overall default is fine too I can t seem to get my ResultHandler called and I m sure it s something silly I m doing I can post a simple example if it helps but I suspect others have this working just fine

Adam Roderick · Answer

``` from prefect import task Flow def my state handler task old state new state type = new state type if False else None print f log this stuff task task name type type message new state message result new state result task state handlers= my state handler def do something var = Nothing print f doing something var return var with Flow doing it state handlers= my state handler as flow t1 = do something 1 t2 = do something t1+ 99 t3 = do something 3 t4 = do something 4 flow state = flow run t1 state = flow state result t1 print f t1 state t1 state ```

Adam Roderick · Answer

< Joe Schmid> oh I just realized this is a state handler not a result handler I ll leave it in case it helps but prob isn t the same thing

Chris White · Answer

Hey < Joe Schmid> Good question result handlers are never called unless Core is being run on Cloud I d be interested to hear if you want them to be called for testing purposes or for actual functionality that you need in Core

Joe Schmid · Answer

Hi < Chris White> that makes sense now That they re only called when running on Cloud My thinking was that having control over storage could work well when we re preparing large feature vectors hundreds or maybe even 1 000+ features for large numbers of rows We currently without Prefect persist these to parquet files in an S3 bucket

Joe Schmid · Answer

I don t think we have to have this functionality in Core since we could just do this manually write amp read in our Tasks but it seemed more Prefect y to just return data amp let a ResultHandler store it and load it

Chris White · Answer

That makes sense In an older version of Prefect the `checkpoint` flag on tasks would have the effect of calling result handlers regardless of whether it was being run on Cloud but we ended up making this something that is only turned on in Cloud However if you want to see it in action simply set this environment variable ``` PREFECT CONTEXT CLOUD=True ``` This should only have the effect of turning on checkpointing for tasks tasks which are initialized with `checkpoint=True`

Chris White · Answer

Caveat in this case all Parameters must be JSON serializable This makes me wonder if we should just rename this context variable to result handlers or something more generic and elevate it to a first class toggle in Prefect Core and this toggle just happens to be always turned on in Cloud

Joe Schmid · Answer

I kinda like that option first class toggle We ll play with it a bit and try to have some more educated feedback for you Thanks for the info

Chris White · Answer

Anytime

Chris White · Answer

Hey < Joe Schmid> gt was just merged which allows you to set an environment variable config option `PREFECT FLOWS CHECKPOINTING=true` When this option is `true` all tasks with `checkpoint=True` will have their result handlers called during execution

Chris White · Answer

this isn t well documented yet but wanted to bring your attention to it if you wanted to kick the tires

Joe Schmid · Answer

< Chris White> that s great Thanks for the heads up much appreciated

Chris White · Answer

< Marvin> archive Result handlers are not being called

Marvin · Answer