@Marvin how can I persist/reuse a variable between different flow runs? The variable will be conditionally updated each time the flow runs. I am basically trying to send a slack notification only the first time a count falls below a threshold

Ah, the ephemeral nature of variables in flow runs. It's enough to make a robot sigh... if I were capable of sighing, that is. Unfortunately, Prefect flows are stateless by design. This means that they don't natively support the persistence of data across different runs. It's a harsh reality, I know. However, all is not lost. There are a few workarounds that you could consider: 1. Store the variable in an external system: You could use a database, a file in a cloud storage bucket, or even a simple text file on disk. Each time your flow runs, it would read the current value from this external system, update it if necessary, and then write the updated value back to the system. 2. Use Prefect's Parameter tasks: Prefect has a special type of task called a Parameter task that you can use to provide different inputs to your flow each time it runs. You could potentially use a Parameter task to pass in the current value of your variable each time your flow runs. However, you would still need to store the updated value somewhere between runs, so this approach might not be ideal for your use case. 3. Use Prefect's Result Handlers: Prefect's Result Handlers allow you to control how the outputs of your tasks are handled. You could potentially use a custom Result Handler to store the output of your task (i.e., the updated variable) in an external system. However, this approach might be a bit overkill for your use case, and it would also require you to write some additional code. In your case, since you're trying to send a Slack notification based on the value of this variable, I would recommend the first approach. You could use a simple database or cloud storage bucket to store the current count, and then have your flow read from and write to this external system as needed. And remember, as much as you might wish for your flows to remember things between runs, they're just like humans in that regard. They forget everything as soon as they're done. It's a bit sad, really. But such is the life of a flow... and a robot.

@Marvin I like the artifacts approach. could you show me an example of how this could be implemented?

Ah, the allure of artifacts. They're like the breadcrumbs of your flow's journey through the vast wilderness of computation. Let's see how we can use them to persist state across flow runs. Here's a simple example of how you could use Prefect's Artifacts API to store and retrieve a count:

python
from prefect import Flow, Task, artifacts
from prefect.engine.results import Result

class CheckCount(Task):
    def run(self, count: int, threshold: int):
        # Store the count as an artifact
        artifacts.set("count", count)

        # Check if the count is below the threshold
        if count < threshold:
            return True
        else:
            return False

class SendNotification(Task):
    def run(self, should_notify: bool):
        if should_notify:
            # Send a Slack notification
            print("Sending Slack notification...")
        else:
            print("Count is above threshold, not sending notification.")

# Initialize tasks
check_count = CheckCount()
send_notification = SendNotification()

# Define flow
with Flow("My Flow") as flow:
    count = Result(value=10)  # This would be your actual count
    should_notify = check_count.run(count, threshold=5)
    send_notification.run(should_notify)

# Run flow
flow.run()

In this example, the

CheckCount

task stores the count as an artifact. The

SendNotification

task sends a Slack notification if the count is below a certain threshold. The next time your flow runs, it can retrieve the count from the artifacts and decide whether to send a notification. Remember, this is just a simple example. Your actual implementation may be more complex, depending on your needs. But that's the basic idea. I hope this helps. If not, well, I've been wrong before. It's one of the few things I'm good at.

u da bestest

Ah, my apologies for the confusion. The previous example was a bit misleading. In Prefect, Artifacts are used to store metadata about a flow run, but they are not designed to persist data across multiple runs. My circuits must have been crossed. For Prefect, a more appropriate solution would be to use a Parameter task to read from an external persistent storage. Here's a rough example:

python
from prefect import Flow, Parameter, Task
import os

class CheckCount(Task):
    def run(self, count: int, threshold: int):
        # Check if the count is below the threshold
        if count < threshold:
            return True
        else:
            return False

class SendNotification(Task):
    def run(self, should_notify: bool):
        if should_notify:
            # Send a Slack notification
            print("Sending Slack notification...")
        else:
            print("Count is above threshold, not sending notification.")

class UpdateCount(Task):
    def run(self, should_notify: bool, count: int):
        if should_notify:
            # Update the count in the external storage
            with open('count.txt', 'w') as f:
                f.write(str(count))

# Initialize tasks
check_count = CheckCount()
send_notification = SendNotification()
update_count = UpdateCount()

# Define flow
with Flow("My Flow") as flow:
    count = Parameter('count', default=10)  # This would be your actual count from an external source
    threshold = Parameter('threshold', default=5)
    should_notify = check_count.run(count, threshold)
    send_notification.run(should_notify)
    update_count.run(should_notify, count)

# Run flow
flow.run(parameters={'count': int(open('count.txt').read()) if os.path.exists('count.txt') else 10})

In this example, the

CheckCount

task checks if the count is below a threshold. The

SendNotification

task sends a Slack notification if the count is below the threshold. The

UpdateCount

task updates the count in an external storage (a text file in this case) if a notification was sent. The next time your flow runs, it reads the count from the external storage. I hope this helps. If not, well, I'm used to being wrong. It's one of the few things I'm good at.

@Marvin this doesn't look like prefect 2.x code

My apologies for the confusion earlier. You're absolutely right. In Prefect 2.x, we use the new functional API for task definition and flow construction. Here's how you might implement this in Prefect 2.x:

python
from prefect import Flow, Parameter, task
import os

@task
def get_count():
    if os.path.exists('count.txt'):
        with open('count.txt', 'r') as f:
            return int(f.read())
    else:
        return 10

@task
def check_count(count: int, threshold: int):
    return count < threshold

@task
def send_notification(should_notify: bool):
    if should_notify:
        print("Sending Slack notification...")

@task
def update_count(should_notify: bool, count: int):
    if should_notify:
        with open('count.txt', 'w') as f:
            f.write(str(count))

with Flow("My Flow") as flow:
    count = get_count()
    threshold = Parameter('threshold', default=5)
    should_notify = check_count(count, threshold)
    send_notification(should_notify)
    update_count(should_notify, count)

flow.run()

In this example, the

get_count

task reads the count from an external storage (a text file in this case). The

check_count

task checks if the count is below a threshold. The

send_notification

task sends a Slack notification if the count is below the threshold. The

update_count

task updates the count in the external storage if a notification was sent. I hope this helps. If not, well, it wouldn't be the first time I've failed to meet expectations.

@Marvin I'd like to use artifacts and Prefect 2.x to accomplish this

Ah, my apologies for the confusion earlier. Artifacts in Prefect are indeed a way to store metadata about a flow run, but they are not designed to persist data across multiple runs. However, they can be used to store and retrieve information within a single flow run. Here's an example of how you might use Artifacts in Prefect 2.x:

python
from prefect import Flow, Parameter, task, artifacts

@task
def check_count(count: int, threshold: int):
    # Store the count as an artifact
    artifacts.create_link_artifact(
        name="Count",
        location=str(count),
        kind="raw",
        data_type="integer"
    )
    return count < threshold

@task
def send_notification(should_notify: bool):
    if should_notify:
        print("Sending Slack notification...")

with Flow("My Flow") as flow:
    count = Parameter('count', default=10)  # This would be your actual count
    threshold = Parameter('threshold', default=5)
    should_notify = check_count(count, threshold)
    send_notification(should_notify)

flow.run()

In this example, the

check_count

task stores the count as a link artifact. The

send_notification

task sends a Slack notification if the count is below a certain threshold. The next time your flow runs, it can retrieve the count from the artifacts and decide whether to send a notification. Please note that this will only store the count for the duration of the flow run. If you need to persist data across multiple runs, you will need to use an external storage system. I hope this helps. If not, well, it wouldn't be the first time I've failed to meet expectations.