How to transmit a simple string from a task to another ?

[EricBoix]

How to reproduce the difficulty

Consider the following workflow where I wish to transmit a simple string from a task to another (in AW I use Value, as opposed to ValueFrom):

# With Hera version 4.4.1
from hera import Parameter, Task, ValueFrom, Workflow

def dummy():
    ...

def consume(msg: str):
    print(f"Message was: {msg}")

with Workflow("io") as w:
    t1 = Task(
        "d", dummy, outputs=[Parameter("msg", value="some_valuable_message")]
    )
    t2 = Task("c", consume, inputs=[t1.get_parameter("msg")])
    t1 >> t2

w.create()

This workflow fails with an error message of the form:
templates.d.outputs.parameters.msg.path must be specified for Script templates

I tried some variations around the outputs argument of the t1 task e.g.

outputs=[Parameter("msg", value=Value("some_valuable_message"))]   # Hey, Value does exist in AW ...
outputs=[Parameter(name="msg", value="some_valuable_message")]
outputs=[Parameter("msg", value={"dummy": "some_valuable_message"})
outputs=[Parameter(name="msg", "some_valuable_message")]
outputs=[Parameter("some_valuable_message")]                     # Lost at sea
outputs=[Parameter(name="msg", default="some_valuable_message")] # Despaired
# Eventually, I gave up on Parameter() and tried another long shot
outputs=[ {"msg": "some_valuable_message"}]
outputs=[ "some_valuable_message" ]
outputs=[ json.dumps({"msg": "ball"}) ]                          # Many variations around that one
# I also tried the artifact way of things but this quickly got out of hand
# because you apparently need to configure some artifact storage (which
# doesn't seem easy to a newbie):
outputs=[RawArtifact("msg", path="/tmp/dummy", data="some_valuable_message")]

Question

My question thus boils down to: how to transmit a simple string arising from the python/Hera context from a task to another task ?

PS: thanks for the good work on Hera and for keeping alive the promise of writing workflows with less suffering than withyaml ;) (although the ArgoWorflows folks still do rock !)

[elliotgunton]

I think the problem is with t2 = Task("c", consume, inputs=[t1.get_parameter("msg")]) - you want to pass an argument to the msg input parameter. i.e. I think t2 = Task("c", consume, arguments={"msg": t1.get_parameter("msg")} will work. See the dag_with_param_passing and dag_with_script_param_passing for examples on how to do this

[EricBoix]

Hi @elliotgunton and thanx for your answer. Following your proposition I thus tried

# Hera version 4.4.2
from hera import Parameter, Task, Workflow

def dummy():
    ...

def consume(msg: str):
    print(f"Message was: {msg}")

### The following workflow tries to transmit a simple string from
# task t1 (as output) to task t2 (as input):

with Workflow("io-", generate_name=True) as w:
    t1 = Task(
        "d", dummy, outputs=[Parameter("msg", value="some_valuable_message")]
    )
    t2 = Task("c", consume, args={"msg": t1.get_parameter("msg")})

    t1 >> t2

w.create()

but with no luck, the error message being

[...] templates.d.outputs.parameters.msg.path must be specified for Script templates

that somehow seems to indicate (templates.d...) that the guilty line would be the definition of task t1 (named d) ?
And thus maybe it is the usage of a Parameter() instance (that doesn't seem to possess a path property) that
triggers the error ?

Lost at sea...

[EricBoix]

Updating code to Hera version 5.6.0. This goes

from hera.workflows import DAG, Parameter, script, Task, Workflow


@script()
def dummy():
    ...


@script()
def consume(msg: str):
    print(f"Message was: {msg}")


with Workflow(generate_name="io-") as w:
    with DAG(name="main"):
        t1: Task = dummy(
            name="t1",
            # Ditch attempt to piggyback some message in the outputs, when
            # the original template didn't have any output (don't ask about
            # the use case since I have to admit it's quite circumvolved).
            outputs=[Parameter(name="msg", value="some_valuable_message")],
        )
        t2: Task = consume(arguments={"msg": t1.get_parameter("msg")})

        t1 >> t2

w.create()

Anyhow, closing this discussion because, with a bit more experience, I now understand they are more Hera-nic ways of getting this type of things done.
Thanx again @elliotgunton