@Marvin I have a retriable task with existing error handling for retriable errors. Can I terminate the execution of the task and trigger the retry behavior with a command during the error handling?

In Prefect, whether it's version 2.x or 3.x, you can indeed control retries through error handling logic by using the

retry_condition_fn

argument. Here's how you can set it up: 1. Define a Custom Retry Handler: Create a callable function that determines if a task should be retried. This function takes three arguments: the task, the task run, and the state of the task run. Depending on the type of error or exception, you can return

True

(triggering a retry) or

False

(preventing a retry). 2. Assign the Retry Handler: Attach this function to a task when defining it, using the

retry_condition_fn

parameter. 3. Example Scenario: - You may want to retry on specific HTTP errors while skipping retries on others. - Define different actions based on exceptions caught during the task's execution. Here's a basic example of how this can be structured:

python
import httpx
from prefect import flow, task

def retry_handler(task, task_run, state) -> bool:
    try:
        state.result()  # Attempt to get the result of the task
    except httpx.HTTPStatusError as exc:
        # Retry if the status code is not 401 or 404
        do_not_retry_on_these_codes = [401, 404]
        return exc.response.status_code not in do_not_retry_on_these_codes
    except httpx.ConnectError:
        # Do not retry
        return False
    except:
        # For any other exception, retry
        return True

@task(retries=1, retry_condition_fn=retry_handler)
def my_api_call_task(url):
    response = httpx.get(url)
    response.raise_for_status()
    return response.json()

@flow
def get_data_flow(url):
    my_api_call_task(url=url)

if __name__ == "__main__":
    get_data_flow(url="<https://httpbin.org/status/503>")

This allows you to specify precise control over what conditions trigger a retry. For more details, refer to the official documentation on Prefect 2.x or Prefect 3.x. These documents provide guidance on setting up task retries in error-handling scenarios.

@Marvin Right now, the task is not entering a Failed state because of the error handling. I want to put the task in a failed state as part of the error handling.

retry_condition_fn

relies on the task being in a Failed state already.

To explicitly set a task to a Failed state as part of your error handling in Prefect, you can return a Failed state from the task function when encountering certain errors. This approach allows you to combine existing error handling with setting a failure state for compatibility with

retry_condition_fn

. Here's how you can implement this: 1. Returning a Failed State: You can return a

Failed

state directly from your task function if certain conditions are met during error handling. This will signal Prefect to transition the task to a Failed state. 2. Example Code for Prefect (both 2.x and 3.x): - Use

from prefect import task, flow

and

from prefect.states import Failed

to import necessary components. - Use custom logic to determine when a task should be marked as failed. Example:

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

@task
def my_task_with_error_handling(condition):
    try:
        # Code that may raise an exception
        if condition:
            raise ValueError("Intentional Error")
    except ValueError as e:
        print(f"Encountered an error: {e}")
        # Return a Failed state explicitly
        return Failed(message="Task failed due to a ValueError.")
    # Normal completion logic
    return "Success"

@flow
def example_flow():
    fail_task = my_task_with_error_handling(True)  # This call will set the task to Failed state
    succeed_task = my_task_with_error_handling(False)  # This call will complete successfully
    print(fail_task, succeed_task)

example_flow()

In this example: - When

condition

is

True

, the task simulates an error and enters a Failed state by returning

Failed(message="Task failed due to a ValueError.")

. - This explicitly using a

Failed

state allows it to be processed by any

retry_condition_fn

you have set up. You can find more details in the Prefect documentation regarding state management and transitioning at: - Prefect 2.x: Concepts of Flows - Prefect 3.x: Manage States This approach should help you integrate error handling with the ability to trigger retries effectively.

@Jason Wiener - I think you just want to return

False

from your retry condition fn if you want to stop retrying and proceed to a Failed state

Thanks @Nate. In this case, the second answer about just forcing the task to Fail in the existing error handling is getting me what I want. The issue was that the error handling was preventing the task from retrying. There are probably some errors where I will want to fail without retries and I see how to use

retry_condition_fn

for those now.