@Marvin in prefect 2, how do i get the result and the status of a submitted task

To retrieve the result and status of a submitted task in Prefect 2, you can use the

State.result()

method to access the result of a task, and you can query the state to get its status. Here is a basic example of how you can use these features: 1. Submit a Task and Retrieve the Result: You can use the

submit()

method to run a task asynchronously and retrieve the result using the

Future.result()

method.

python
   import asyncio
   from prefect import flow, task

   @task
   async def my_task():
       return 1

   @flow
   async def my_flow():
       future = await my_task.submit()  # Submit the task
       result = await future.result()   # Retrieve the result
       return result + 1

   result = asyncio.run(my_flow())
   assert result == 2

This code demonstrates submitting a task and retrieving its result once it completes. More details are available in the Prefect documentation here. 2. Check Task Status: To check the status of a task, you can use the task's state. Prefect provides ways to retrieve the task state and status after it has been executed.

python
   import asyncio
   from prefect import flow, task

   @task
   async def my_task():
       return 1

   @flow
   async def my_flow():
       state = await my_task(return_state=True)  # Get the task state
       result = await state.result(fetch=True)   # Retrieve the task result
       status = state.state                      # Get the task status
       print(f"Task Status: {status}")
       return result + 1

   asyncio.run(my_flow())

Here,

state.state

gives you the current status of the task, and

await state.result(fetch=True)

retrieves the result. To ensure consistent behavior, Prefect 2.6.0 added automatic retrieval of persisted results. You might want to look into this feature if you plan to use result persistence. Lastly, if you experience any issues with task execution or retrieval, the Prefect GitHub issues page is an excellent resource for troubleshooting similar problems Prefect GitHub Issues. Feel free to reach out if you have any more questions or need further assistance!

@Marvin check if task state is Completed

In Prefect 2, you can check if a task state is

Completed

by comparing the state's type to

COMPLETED

. States in Prefect have types and names that reflect their current condition, and

COMPLETED

is one of the terminal state types. Here's how you might typically check if a task's state is `Completed`:

python
from prefect import task, flow
from prefect.states import Completed

@task
def my_task():
    return "result"

@flow
def my_flow():
    state = my_task(return_state=True)
    
    # Check if the task state is Completed
    if state.type == Completed.type:
        print("Task is completed!")
    else:
        print("Task is not completed.")

my_flow()

This example demonstrates how to access the task's state type and verify if it matches

Completed

. For more information on states, you can refer to the Prefect documentation on states.

@Marvin using PrefectFutures and a submitted task, print out the task result as well as check if state is completed. if it is not then print out the state

To handle a submitted task using

PrefectFuture

and print the result while checking if the task state is

Completed

, you can use the

result()

method to get the result and the state's type to verify its status. Here's how you can do this in Prefect 2:

python
import asyncio
from prefect import flow, task
from prefect.states import Completed

@task
async def my_task():
    return "Task Result"

@flow
async def my_flow():
    # Submit the task and retrieve the PrefectFuture
    future = await my_task.submit()
    
    # Retrieve the result from the future
    result = await future.result()
    print(f"Task Result: {result}")
    
    # Check the task's state
    state = future.get_state()
    if state.type == Completed.type:
        print("Task state is Completed.")
    else:
        print(f"Task state is not Completed. Current state: {state}")

asyncio.run(my_flow())

Here's a breakdown of what's happening: - Submit the Task:

await my_task.submit()

submits the task and returns a

PrefectFuture

. - Get Result:

await future.result()

retrieves the result of the task once completed. - Check State:

future.get_state()

gets the current state of the task, which allows you to check if it is

Completed

or some other state. If it is not

Completed

, it prints the current state. To learn more about

PrefectFuture

and how it can be used to manage task states and results, please check out Prefect's documentation on task runners.