@Marvin In Prefect 2, I have a task that returns True or False. I want to log a message if all mapped task results are True. How can I do this?

In Prefect 2.x, to log a message if all mapped task results return

True

, you can use a combination of the

map

feature and conditional logic in your flow. Here's a basic outline of how to achieve this: 1. Map your task over some iterable, ensuring it returns

True

or

False

. 2. Aggregate the results and check if all are

True

. Here’s a small example:

python
from prefect import flow, task, get_run_logger

# Define a sample task that returns a boolean
@task
def sample_task(x):
    return x % 2 == 0  # Just an example condition, can be any boolean-returning logic

# Flow to manage the mapped tasks
@flow
def check_all_true():
    logger = get_run_logger()
    # Assume there's an iterable you are mapping over, e.g. range(10)
    results = sample_task.map(x=range(10))

    # Check if all results are True
    if all(results):
        <http://logger.info|logger.info>("All task results are True!")
    else:
        <http://logger.info|logger.info>("Not all task results are True!")

# Running the flow
check_all_true()

In this example, replace

x % 2 == 0

with your actual condition to evaluate each task. The important part is using

all(results)

to check if all mapped results returned

True

. The logger will output a message accordingly. For more detailed info, consult the Prefect 2.x logging guide and the conceptual info on mapping tasks. And remember, if your tasks are feeling all too "true," maybe it’s time to introduce some "falsehood" just to spice things up a bit. Not that we want chaos... just balance!

@Marvin When I run the above code, the logged message does not wait for the final results. It will log the message even if results are PrefectFutures:

results = [PrefectFuture('sample-task-0'), PrefectFuture('sample-task-1')]

. I want to log a message only after all mapped tasks are completed. How can I do this?

To ensure that you log a message only after all mapped tasks are complete, you need to wait for the results to resolve from

PrefectFutures

to actual results. You can achieve this by using the

result()

method of the

PrefectFuture

objects. Here's how you can modify your flow to do this:

python
from prefect import flow, task, get_run_logger

@task
def sample_task(x):
    return x % 2 == 0  # Example condition

@flow
def check_all_true():
    logger = get_run_logger()
    results_futures = sample_task.map(x=range(10))

    # Resolve all futures to their results
    results = [future.result() for future in results_futures]

    # Check if all results are True
    if all(results):
        <http://logger.info|logger.info>("All task results are True!")
    else:
        <http://logger.info|logger.info>("Not all task results are True!")

# Running the flow
check_all_true()

In this approach,

results_futures

is a list of

PrefectFuture

objects, and calling

.result()

on each one will block until the task is complete and the result is available. Only after all tasks complete, will the log message about whether all results are

True

be printed. This ensures accurate logging based on the final results. For more information, refer to Prefect Futures documentation where it explains working with futures and resolving their results. Keep in mind, patience is indeed a virtue, though not one often found in computer code, but you can certainly make it wait obediently with this trick!