How to respond to state changes

from prefect import flow
from prefect.blocks.core import Block
from prefect.settings import get_current_settings


@flow(retries=1)
def failing_flow():
    raise ValueError("oops!")


@failing_flow.on_failure
def notify_slack(flow, flow_run, state):
    slack_webhook_block = Block.load(
        "slack-webhook/my-slack-webhook"
    )

    PREFECT_API_URL = get_current_settings().api.url

    slack_webhook_block.notify(
        (
            f"Your job {flow_run.name} entered {state.name} "
            f"with message:\n\n"
            f"See <https://{PREFECT_API_URL}/flow-runs/"
            f"flow-run/{flow_run.id}|the flow run in the UI>\n\n"
            f"Tags: {flow_run.tags}\n\n"
            f"Scheduled start: {flow_run.expected_start_time}"
        )
    )

if __name__ == "__main__":
    failing_flow()

from prefect import flow, task
import time

def record_start_time(task, task_run, state):
    print(f"Task {task.name} started at {time.time()}")

@task(on_running=[record_start_time])
def my_task():
    return "hello"

# Or use the decorator pattern
@task
def another_task():
    return "world"

@another_task.on_running
def log_start(task, task_run, state):
    print(f"Starting {task.name}!")

@flow
def my_flow():
    my_task()
    another_task()

from prefect import flow
from prefect.logging.loggers import flow_run_logger


def my_hook(flow, flow_run, state):
    logger = flow_run_logger(flow_run, flow)
    logger.info(f"Flow {flow_run.name} entered state {state.name}")


@flow(on_failure=[my_hook])
def failing_flow():
    raise ValueError("oops!")

from functools import partial
from prefect import flow, task

data = {}

def my_hook(task, task_run, state, **kwargs):
    data.update(state=state, **kwargs)

@task
def bad_task():
    raise ValueError("meh")

@flow
def ok_with_failure_flow(x: str = "foo", y: int = 42):
    bad_task_with_a_hook = bad_task.with_options(
        on_failure=[partial(my_hook, **dict(x=x, y=y))]
    )
    # return a tuple of "bar" and the task run state
    # to avoid raising the task's exception
    return "bar", bad_task_with_a_hook(return_state=True)

_, task_run_state = ok_with_failure_flow()

assert data == {"x": "foo", "y": 42, "state": task_run_state}