Hi, is there any more document on parameters? other than here: https://docs.prefect.io/core/concepts/parameters.html, I’m having a confusing time getting them to work especially when I need multiple

Hi @John Faucett - could you describe the pain points you’re having? Ultimately Parameters are just a special type of Task so they have the same imperative interface

hi @Chris White thanks for the response. Yes, I guess its just not clear to me how to add multiple parameter dependencies for a task, and pass results of task computations as parameters further downstream to other tasks

so for example,

with Flow("parameter-example") as flow:
    p, q = Parameter("p"), Parameter("q")
    result = my_task(input_kwarg=p, another_kwarg=q)

ah ok, right now I had

my_task.set_upstream(my_param, flow=flow, key='my_param_name')

that works as well!

but what about when my task needs both p and q?

yea, ultimately you’re binding the results of the upstream tasks / parameters to the keyword arguments of the downstream task’s run method, so the order isn’t important

ok nice. Thanks for the help. I just have one other question? Is there a way to set which task should be run first?

anytime! yea sure, just set the appropriate dependencies. So for example, if you want A to run before B, all you need to do is:

task_b.set_upstream(task_a, flow=flow)

in this case, no data is exchanged but there is now an enforced dependency relationship. You can also see these relationships with

flow.visualize()

for easier introspection

oh nice, and if I do

task_b.set_upstream(task_a, flow=flow)
task_b.set_upstream(task_c, flow=flow)

will it wait for both upstreams to finish?

yup exactly!

sweet! I must say I’m really liking prefect a lot

awesome - thank you! if you have any other questions or need further clarification we’re always here to help!

well, I’m testing prefect out to see if we can use it to replace some luigi pipelines right now so I’m sure I’ll probably be taking you up on that one 🙂

oh awesome! If you collect any notes on the pros / cons of the replacement we’d love to hear them and I’m sure other people would as well

ok yea thats a good idea, right now I’m liking state a lot over saving output files, thats nice