Hi, community I am studying how workflow works and found that

@workflow
def my_wf() -> str:
    print("@@@ i am in")
    res = say_hello()
    return res

if I execute it locally,

@@@ i am in
@@@ i am in

Will appear in my terminal Can anyone explain why or guide me some reference ? Thanks a lot !

Hey @L godlike, I'm guessing your task

say_hello

also has the same print statement in it?

No it doesn’t But thanks a lot for your help !

Same here, you can assume say_hello return a string “hello” It will print the @@ I am in twice

Would you care to show the code for

say_hello

?

sure, following is the code.

def say_hello():
    return "hello"

@workflow
def my_wf() -> str:
    print("@@@ i am in")
    res = say_hello()
    return res

my_wf()

Ahh okay, and you're executing with

pyflyte run

?

just run it locally.

In my understanding: 1. first print: happened because flytekit compiles the workflow to DAG 2. second print: happened at run time.

Yeah I don't think you need to call it explicitly at the bottom of the script. If you remove

my_wf()

it should work as expected

If you also print the

res

, the first print will be promise, the second print will be flytekit literal.

I see, looks like the compile will also trigger the print function. if I change the code to the following, it will print 5 line, 4 from my_wf, 1 from last line. Does this result meet yours expectation? @Yicheng Lu @Pryce

@workflow
def my_wf() -> str:
    print("@@@ i am in")
    res = say_hello()
    print(type(res))
    return res

print(my_wf())

Yes. Do you see that the first type (res) printed is a promise, while the second is actually a literal?

Not really, that’s an another topic, it simply print.

@@@ i am in
<class 'str'>
@@@ i am in
<class 'str'>
hello

Can you try print(res)?

@@@ i am in
hello
@@@ i am in
hello
hello

Not sure if it’s related to the env I run

Hmm interesting, I was expecting one of the print(type(res)) to be a promise. I guess it depends how you're executing, if it's just with

python

or

pyflyte run

. But otherwise expected.. if you remove the

()

from

print(my_wf())

you should only get one print loop.

my bad

YES!!!

Yeah that makes more sense

when we compile, we should get a promise, however, if we get the 2nd at run time => we should get the literal, right?

Yes - the literal value will be produced at run time instead of the promise

Thanks for your explaination! @Pryce @Yicheng Lu Thanks!

Also checkout the

pyflyte run

vs

python

section here that describes the different ways of running locally, if you haven't seen it yet.. https://docs.flyte.org/projects/cookbook/en/latest/index.html

Thanks for the help!

No worries!

you should not use print in the workflow. @workflow is used to define your DAG. when you run the workflow on flyte cluster, flyte will only run each individual task (say_hello) in the pod, and won’t run workflow function (my_wf). if you want to use print, for loop in the workflow, you can use @dynamic.

Thanks a lot for @Pryce @Yicheng Lu @Hank Huang @Kevin Su your guys help ! I will absorb those knowledge !