Tasks sequence in Prefect Flow Python

Question

I'm currently working with the Python framework - Prefect (prefect.io) I wrote the code below

from prefect import Flow, task
@task
def say_hello():
    print('Hello')

@task
def say_how_a_u():
    print('How are you?')

@task
def say_bye():
    print('Bye Bye')

with Flow('Test') as flow:
   say_hello()
   say_how_a_u()
   say_bye()

flow.run()

The fact is that all functions are called in parallel. How to make one function call after another and waited for the previous function? hello -> how_a_u -> bye

I work with triggers, but it fail

Answer 1

You can just specify the upstream dependencies during the Flow block. There is another syntax you can find here

from prefect import Flow, task
@task
def say_hello():
    print('Hello')

@task
def say_how_a_u():
    print('How are you?')

@task
def say_bye():
    print('Bye Bye')

with Flow('Test') as flow:
   a = say_hello()
   b = say_how_a_u(upstream_tasks=[a])
   c = say_bye(upstream_tasks=[b])

flow.run()