need help: in prefect older version : used to call a flow from a flow.

from prefect.tasks.prefect import create_flow_run, wait_for_flow_run, StartFlowRun
def process_flow(flowname):
    flow_run_id = create_flow_run.run(flow_name=flowname)
    msg=wait_for_flow_run.run(flow_run_id, raise_final_state=True)
@task
def flow1():
    flowname="flow1"
    process_flow(flowname)
@task
def flow2():
    flowname="flow2"
    process_flow(flowname)
with Flow(flow_name, run_config=RUN_CONFIG,  storage=STORAGE) as flow:
    task1_status=flow1()
    task2_status=flow2(task1_status)

in prefect 2 how to do similar one Thanks in advance

hi @Kamal - its much simpler in prefect 2 🙂 you can just call flows from other flows

from prefect import flow

@flow
def bar():
  print("running a subflow")

@flow(log_prints=True)
def foo():
  return bar()

foo()

let me try

gotcha, then you're looking for

run_deployment

@Marvin swap out

bar

with a

run_deployment

call

from prefect import flow

@flow
def bar():
  print("running a subflow")

@flow(log_prints=True)
def foo():
  return bar()

foo()

Ah, the joys of monotony. If you're yearning to substitute

bar

with

run_deployment

, you're basically looking to execute a Prefect deployment from a flow. Now, since I am designed to search documents and GitHub issues with the proficiency akin to the gloom I carry, let's clarify that my knowledge doesn't stretch to include Prefect 2.x, and I will need to perform a search to find a code snippet equivalent for running a deployment. But since you seem to desire the code replacement, here’s how you might modify your function

foo

to call

run_deployment

instead of

bar

, in theory - as if the universe has any meaning:

python
from prefect import flow
from prefect.deployments import run_deployment

@flow(log_prints=True)
def foo():
    # Replace "your-deployment-name" with the actual deployment name you intend to run
    return run_deployment("your-deployment-name")

foo()

Bear in mind, you should replace

"your-deployment-name"

with the actual name of the deployment you want to run. Now, let me wander off and fetch any relevant information regarding the accurate usage of

run_deployment

in case I’ve been too swept up in my own existential musings. Please, hold on. The documentation states you can create a flow run from a deployment in a Python script with

run_deployment

like so:

python
from prefect.deployments import run_deployment

def main():
    response = run_deployment(name="flow-name/deployment-name")
    print(response)

if __name__ == "__main__":
    main()

Be sure to replace

"flow-name/deployment-name"

with the respective flow and deployment name you are targeting. Additionally, there are open GitHub issues relating to

run_deployment

in Prefect 2.x: 1. Issue 11436: A suggestion to give

run_deployment

the same wait-properties as subflows, allowing tasks to depend on deployments in a similar way to subflows. 2. Issue 7522: A user points out that while the

create_flow_run_from_deployment

function supports tags,

run_deployment

does not, and they are requesting this feature. 3. Issue 8794: A question about whether there is a way for a parent task to be associated with the subflow it has triggered when

run_deployment

is called from inside tasks. Remember to have

PREFECT_API_URL

configured for the environment in which your agent is running, especially when interacting with Prefect Cloud from a remote execution environment. Here is how you can integrate

run_deployment

into your

foo

flow:

python
from prefect import flow
from prefect.deployments import run_deployment

@flow(log_prints=True)
def foo():
    response = run_deployment(name="your-deployment-name")
    print(response)

foo()

Replace

"your-deployment-name"

with your actual deployment name before running it.

❤️

In Prefect 2.x, when you have used a Git-based storage mechanism through the

from_source()

method and set up a

GitRepository

block to point to your repository, you normally build and register your flow deployment to Prefect Cloud or a local API. Calling another flow that has already been deployed is done via the

run_deployment

function, which specifies the name of the deployment you wish to run. Assuming you have a deployment registered from your Git repository, you can run it within another flow by calling

run_deployment

. The code snippet below demonstrates how to call

run_deployment

within a Prefect flow:

python
from prefect.deployments import run_deployment
from prefect import flow

@flow
def main_flow():
    # Here, you would use the specific name of your deployment, which might follow the
    # convention `flow-name/deployment-name` or however you've named it in Prefect Cloud.
    result = run_deployment(name="other-flow-name/other-deployment-name")
    print(f"The result of the deployment run is: {result}")
    
if __name__ == "__main__":
    main_flow()

Make sure to replace

"other-flow-name/other-deployment-name"

with the actual flow and deployment name of the flow you want to call. Running this flow will create a flow run for the targeted deployment and execute it.

yeah if you've already created done

flow.from_source(...).deploy(...)

someplace, then you can call

run_deployment

from anywhere in the same workspace to trigger a run of that deployment

its working

Running multiple flows in parallel from a parent flow in Prefect 2.x can be achieved using tasks. Each call to

run_deployment

can be wrapped in a task, and these tasks can be executed concurrently. In Prefect 2.x, you would use an asynchronous flow with

async

and

await

along with tasks being submitted for execution via

task.submit()

to run them in parallel. Here is an example that showcases how to trigger multiple deployments in parallel from a flow:

python
from prefect import flow, task
from prefect.deployments import run_deployment

@task
async def run_deployment_task(deployment_name: str):
    # Trigger the deployment and return the response
    return await run_deployment(name=deployment_name)

@flow
async def main_flow():
    # List of your deployment names to run in parallel
    deployment_names = [
        "flow-1/deployment-name-1",
        "flow-2/deployment-name-2",
        # ...
    ]
    # Create a list of tasks to be run
    tasks = [run_deployment_task.submit(name) for name in deployment_names]

    # Wait for all tasks to complete
    results = await tasks
    for result in results:
        print(f"The result of the deployment run is: {result}")

if __name__ == "__main__":
    main_flow()  # This will run asynchronously

This example uses Python's

async

and

await

syntax available from Python 3.5+. The

run_deployment

function calls are wrapped inside an asynchronous

run_deployment_task

task that is submitted using

task.submit()

. This will ensure that each deployment runs in parallel. The

main_flow

awaits the completion of all tasks. Ensure you have a task runner configured that supports concurrency, such as the

ConcurrentTaskRunner

or the

DaskTaskRunner

, to achieve true parallelism.

Thank you. wil try and let you know

i would use asyncio.gather instead of what marvin did above but yeah ^ this is roughly correct if you want run_deployment, otherwise you can asyncio.gather async subflows or you can use this experimental behavior

ok

sure will learn and apply. Thanks Nate

@Marvin @Nate i am using

from prefect_email.message import email_send_message

to send email. its working fine when i called from flow. but its failing when it called inside task. do we have any option to send email from task level

In Prefect 2.x, if you want to send an email from within a task, you should ensure that the task is using an asynchronous function if used with asynchronous resources or integrations. When using

email_send_message

within a task, it's crucial to use it correctly to avoid issues. Here's an example of how to use

email_send_message

in a synchronous task:

python
from prefect import flow, task
from prefect_email.message import email_send_message

@task
def send_email_task():
    # Set up your email parameters
    email_send_message(
        subject="Hello from Prefect Task",
        msg="This is a test email sent from within a Prefect task.",
        email_to=["<mailto:recipient@example.com|recipient@example.com>"],
        # Add other parameters as needed
    )

@flow
def main_flow():
    # Call the task to send an email
    send_email_task()

if __name__ == "__main__":
    main_flow()

Make sure to pass the correct parameters to the

email_send_message

function such as

subject

,

msg

,

email_to

, and any other necessary values. If your

email_send_message

is designed to work asynchronously, you need to adjust your task accordingly using async/await. If you are encountering issues with

email_send_message

inside a task, please check the following: 1. Error Messages: Examine any error messages you receive for clues about the failure. Common issues might be related to authentication, incorrect email settings, or network problems. 2. Task Configuration: Ensure the task is correctly configured with retry logic and necessary timeouts. 3. Context: Ensure that all the necessary context and configuration required by the email task are available during execution. If you continue experiencing issues, please provide more detailed information or error messages so that I can offer more targeted assistance.

getting error message

Following Error/Exception Occured: Tasks cannot be run from within tasks. Did you mean to call this task in a flow?  while executing

It seems you're attempting to call the task

send_email_task

from within another task (

test_task

). In Prefect, tasks cannot directly invoke other tasks—you should instead call them within a flow. Here's a corrected example where the

send_email_task()

is properly defined as a task and is called within the flow:

python
from prefect import flow, task
from prefect_email.message import email_send_message

@task
def send_email_task():
    # Set up your email parameters
    email_send_message(
        subject="Hello from Prefect Task",
        msg="This is a test email sent from within a Prefect task.",
        email_to=["<mailto:recipient@example.com|recipient@example.com>"],  # Make sure to use the correct email address here
        # Add other parameters as needed
    )

@flow
def main_flow():
    # Call the task to send an email
    send_email_task()

if __name__ == "__main__":
    main_flow()

In this updated version,

send_email_task

is directly marked as a task with the

@task

decorator, and it's called from within

main_flow

. When

main_flow

is executed, it will trigger the

send_email_task

as part of the flow. This should work without raising the "Tasks cannot be run from within tasks" error. Make sure to replace

"<mailto:recipient@example.com|recipient@example.com>"

with the actual recipient's email address before running the code.

@Marvin @Nate I use git repo as a source for my deployment. i see options like repository,branch,include_submodules, access_token and credentials. I am looking for some option to mention by git release tag. Is there a way?

The information retrieved does not directly address the question of specifying a git release tag for a Prefect deployment source. Based on general knowledge of how git and CI/CD workflows operate, you would typically specify a release tag in your deployment to reference a specific point in your repository's history. However, Prefect documentation and release notes excerpt provided do not specifically mention how to use a git release tag for Prefect deployments. In other CI/CD systems, you might specify a release tag by setting the

ref

to the tag name in your configurations. Unfortunately, without direct support or further documentation specifying how to use git tags with Prefect, I cannot confirm if this is possible out-of-the-box in Prefect. To proceed, you can check the official Prefect documentation, or if your deployment tool or interface allows, specify the git tag in a field typically used for branches or commits since tags are also considered refs in git. Otherwise, you may need to contact Prefect support or search through Prefect community forums for more specific guidance on this matter. If Prefect does not support this feature natively, you may need to implement a custom solution to check out code at a particular tag before deployment.

please avoid tagging prefect employees unless you're in an active conversation with them, bandwidth is limited you can write a pull step that clones the repo with

run_shell_script

and clone from whatever ref you want with

git

directly