Hi How can I execute a map inside a task Something like this

Question

Hi How can I execute a map inside a task Something like this code in thread

William Jamir · Answer

I m using Prefect 1 ```from prefect import Flow task task def task 1 task 2 run task 3 map range 2 task def task 2 print 2 task def task 3 x print x with Flow name= a as flow task 1 flow run ``` When running this code I m receiving ``` Could not infer an active Flow context while creating edge to lt Task task 3 gt This often means you called a task outside a `with Flow ` block If you re trying to run this task outside of a Flow context you need to call `task 3 run ````

Anna Geller · Answer

you need to call mapping within your Flow not within a task so this line needs to move to Flow ```task 3 map range 2 ``` also you really shouldn t have to do ```task 2 run ``` instead call task 2 in your Flow

Anna Geller · Answer

also < William Jamir> can you move the code into the thread

William Jamir · Answer

< Anna Geller> Sure code moved to thread gt you need to call mapping within your Flow not within a task so this line needs to move to Flow Ah okay so sorry if I did not make my intention clear I explicitly want to call a map from inside a task in order if possible to make my task composable So is impossible limitation to call a `map` inside a task like we do with task 2 run gt instead call task 2 in your Flow Yeap indeed sorry if my intention was not clear I only called `task 2` like this in order to show that I was trying to compose my tasks to be reusable Taking advantage of this message can I execute tasks like this with run inside another task or its not recommended I mean is there any drawback that I should be aware on calling tasks like this

Anna Geller · Answer

gt is impossible limitation to call a `map` inside a task like we do with task 2 run It s not a limitation it s an intentional design decision from Prefect engineers to trigger mapped tasks from a flow rather than from a task what are you trying to do here if you want to chain them so that mapped runs after it you would use `upstream tasks` keyword if the problem is to make some code reusable you can build it as custom functions that you can package into a Python package module and then call from within your tasks

Anna Geller · Answer

gt can I execute tasks like this with run inside another task or its not recommended Great question it s indeed not recommended to run tasks from other tasks The drawback is lack of visibility you don t see such a task in any of your workflow schematics makes your code less composable since it s not clear what calls what and makes it harder to maintain since there is a mix of responsibility the task is no longer responsible for one thing Prefect encourages small tasks since this makes things easier to build troubleshoot and maintain