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<@ULVA73B9P> How can I programmatically detect if ...
# ask-marvin
t
@Marvin How can I programmatically detect if a prefect flow is a subflow from within a subflow or a task called by that subflow?
m
To programmatically detect if a flow is a subflow or if a task is called by a subflow within Prefect, you can look at the 
state_details
of the flow or task run. Specifically: - A task that represents a subflow will have a 
child_flow_run_id
field in its 
state_details
. - A subflow can be identified by the presence of a 
parent_task_run_id
in its 
state_details
. Here's an example of how you might implement this in Prefect:
Copy code
python
from prefect import flow, task, get_run_context

@task
def detect_if_subflow():
    context = get_run_context()
    if context.flow_run.state_details.parent_task_run_id:
        print("This flow is a subflow.")
    else:
        print("This flow is not a subflow.")

@flow
def subflow_example():
    detect_if_subflow()

@flow
def parent_flow():
    subflow_example()

if __name__ == "__main__":
    parent_flow()
In this example: 1. The 
detect_if_subflow
task checks the 
state_details
of the current flow run to see if it has a 
parent_task_run_id
. 2. If 
parent_task_run_id
is present, it indicates that the current flow is a subflow. For more details, you can refer to the Prefect documentation on flows. Happy subflow detecting! Or as happy as one can be in the vast, incomprehensible universe. Is there anything else you need?
t
@Marvin That failed with this error: File "/workspace/.venv/lib/python3.10/site-packages/prefect/_internal/concurrency/calls.py", line 352, in _run_sync result = self.fn(*self.args, **self.kwargs) File "/workspace/gpt_candidate/v2/setup.py", line 83, in setup_telemetry job_id = flow_run.get_parent_flow_run_id() if detect_if_subflow() else flow_run.get_id() File "/workspace/gpt_candidate/v2/setup.py", line 77, in detect_if_subflow if context.flow_run.state_details.parent_task_run_id: AttributeError: 'TaskRunContext' object has no attribute 'flow_run' I need to be able to call the "detect_if_subflow" function from within a task called by the subflow.
m
Based on the updated information, it appears that in Prefect, you should explicitly obtain the flow run context and access its state details to check if it is a subflow from within a task. Here's how you can do it within a task: 1. Access the Flow Run Context: Use 
FlowRunContext.get()
to retrieve the flow run context explicitly. 2. Check for 
parent_task_run_id
: Look for the 
parent_task_run_id
in the flow run's 
state_details
to determine if it's a subflow. Here is the corrected implementation:
Copy code
python
from prefect import flow, task
from prefect.context import FlowRunContext

@task
def detect_if_subflow():
    flow_run_ctx = FlowRunContext.get()
    if flow_run_ctx and flow_run_ctx.state_details.parent_task_run_id:
        print("This flow is a subflow.")
        return True
    else:
        print("This flow is not a subflow.")
        return False

@flow
def subflow_example():
    detect_if_subflow()

@flow
def parent_flow():
    subflow_example()

if __name__ == "__main__":
    parent_flow()
This implementation ensures that from within the 
detect_if_subflow
task, you correctly access the flow run context and its state details. With this approach, you should be able to detect if the flow is a subflow even when the task is called by a subflow. For more guidance, refer to the Prefect documentation on runtime contexts which provides further details on these concepts.
t
@Marvin Got this error trying that: AttributeError: 'EngineContext' object has no attribute 'state_details' Again, I need to be able to call "detect_is_subflow" from a prefect task
m
To programmatically detect if a flow is a subflow from within a 
task
in Prefect, you need to check the 
parent_task_run_id
of the flow run context. Here’s the corrected implementation taking into account that 
TaskRunContext
doesn't support 
state_details
. Instead, we're going to focus on retrieving the 
flow_run
context: 1. Access the Task Run Context: Use 
get_run_context()
to retrieve the context. 2. Check for Parent Flow Attributes: Determine from the 
parent_task_run_id
if this flow is part of a subflow. Here is an example:
Copy code
python
from prefect import flow, task, get_run_context
from prefect.context import FlowRunContext, TaskRunContext

@task
def detect_if_subflow():
    context = get_run_context()
    if isinstance(context, TaskRunContext):
        flow_run = context.task_run.flow_run
        if flow_run.parent_task_run_id:
            print("This flow is a subflow.")
            return True
        else:
            print("This flow is not a subflow.")
            return False
    else:
        print("Context is not a TaskRunContext.")
        return False

@flow
def subflow_example():
    detect_if_subflow()

@flow
def parent_flow():
    subflow_example()

if __name__ == "__main__":
    parent_flow()
In this example: 1. Access Run Context: The 
get_run_context()
function is used to access the current run context. 2. Check Parent Flow ID: Within the 
TaskRunContext
, check the associated `flow_run`'s 
parent_task_run_id
to see if this is a subflow. Running this code should allow you to programmatically detect if a flow is a subflow from within a task. For reference, check the Prefect documentation on runtime contexts for additional information. Let me know if there's anything else you'd like to dive into!
t
@Marvin Getting this now: AttributeError: 'TaskRun' object has no attribute 'flow_run'. Did you mean: 'flow_run_id'?
m
It appears that accessing the flow run from the task run context is slightly different. Instead, you should use the 
flow_run_id
to fetch the flow run details. Here is a refined approach: 1. Access the Task Run Context: Use 
get_run_context()
to retrieve the context. 2. Fetch Flow Run Details: Use the Prefect client to retrieve the flow run details using the 
flow_run_id
. Here's the updated implementation:
Copy code
python
from prefect import flow, task, get_run_context
from prefect.client import get_client

@task
async def detect_if_subflow():
    context = get_run_context()
    if context:
        task_run = context.task_run
        flow_run_id = task_run.flow_run_id
    
        async with get_client() as client:
            flow_run = await client.read_flow_run(flow_run_id)
        
        if flow_run.parent_task_run_id:
            print("This flow is a subflow.")
            return True
        else:
            print("This flow is not a subflow.")
            return False
    else:
        print("No context available.")
        return False

@flow
def subflow_example():
    detect_if_subflow()

@flow
def parent_flow():
    subflow_example()

if __name__ == "__main__":
    parent_flow()
In this corrected code: 1. Access Run Context: Using 
get_run_context()
, you access the current context. 2. Fetch Contextual Data: Retrieve the 
flow_run_id
from the 
task_run
context. 3. Prefect Client: Use the Prefect client to read the flow run details by 
flow_run_id
. 4. Check for Parent ID: Check if the 
parent_task_run_id
is present to determine if this is a subflow. This solution should work seamlessly for detecting if a flow is a subflow within a task. For further details, you might consult the Prefect API documentation.
t
Nevermind, this works:
Copy code
job_id = flow_run.parent_flow_run_id if flow_run.parent_flow_run_id else flow_run.id
I forgot to decorate my parent flow facepalm
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