@Marvin For Prefect 2.x how do I set a flow to wait for another flow?

Oh, chaining flows now, are we? I'll look it up. One moment, please. To make a flow wait for another flow in Prefect 2.x, you can use the

wait_for

parameter. This parameter allows you to specify upstream dependencies, ensuring certain tasks or entire flows wait for others to complete before proceeding. Here are some examples and important points: ### Using

wait_for

in Tasks and Flows You can make tasks or subflows wait for other tasks' results by using the

wait_for

parameter.

python
from prefect import flow, task

@task
def task_a():
    print("Task A completed")

@task
def task_b():
    print("Task B completed")

@flow
def dependent_flow():
    task_a_result = task_a.submit()
    task_b_result = task_b.submit(wait_for=[task_a_result])

In this snippet: -

task_b

will wait for

task_a

to complete before running. ### Pausing Flow Execution You can pause a flow and resume it later, a method useful for out-of-process suspensions.

python
from prefect import flow, pause_flow_run, resume_flow_run, task

@task(persist_result=True)
def example_task():
    return 42

@flow(persist_result=True)
def pausing_flow():
    result = example_task.submit()
    pause_flow_run(timeout=30, reschedule=True)
    # Wait for the flow to resume
    example_task(wait_for=[result])

- Use

pause_flow_run

to suspend a flow, which can later be resumed using

resume_flow_run

. ### Subflows and Upstream Dependencies Upstream dependencies apply to all tasks, subflows, and mapped tasks submitted.

python
from prefect import flow, task

@flow
def parent_flow():
    result = upstream_flow.submit()
    downstream_flow.submit(wait_for=[result])

@flow
def upstream_flow():
    print("Upstream flow")

@flow
def downstream_flow():
    print("Downstream flow, waits for upstream flow")

This way,

downstream_flow

will wait for the

upstream_flow

to complete. For more details, check out the Prefect 2.x documentation on flows and the guide on specifying upstream dependencies. Hope this helps!