https://prefect.io
Join Slack
Do Parameters work for Task that are classes and not functions? <https://docs-v1.prefect.io/core/con...
# ask-community
m
Do Parameters work for Task that are classes and not functions? https://docs-v1.prefect.io/core/concepts/parameters.html I am trying to pass a Parameter to a ShellTask but it does not look like it works. Any example of that?
1️⃣ 1
✅ 1
Copy code
shell_task = ShellTask(
    log_stdout=True,
    log_stderr=True,
    stream_output=True,
)

with Flow(
    "model_on_demand",
) as flow:
    select = Parameter("select", required=True)
    shell_task(command=f"echo '{select}'")
This returns the class and not the value of the Parameter ...
b
Hi Matt, this user asked a similar question. They were able to have the custom task accept the parameter value via the .run() method. Let us know if the example helps.
m
So the solution is to 
run()
the Parameter (which is a Task) But it's not recognized as an "input" so I cannot trigger the flow with different values of the Parameter in the Web UI So I don't believe that this is a good solution. Maybe I don't understand it
b
After reviewing this with the team, the following example should work for you:
Copy code
shell_task = ShellTask(
    log_stdout=True,
    log_stderr=True,
    stream_output=True,
)

@task
def generate_command(select):
   return f"echo '{select}'"

with Flow(
    "model_on_demand",
) as flow:
    select = Parameter("select", required=True)
    shell_task(command=generate_command(select))
The string for the command needs to be set within a task. It can't be set within the 
with Flow(…)
block because nothing has values at that point.
m
will try that. Thank you
So it sounds like it works for 
ShellTask
but not for 
DbtShellTask
which is a child of it ...
Copy code
class DbtShellTask(ShellTask):
    pass
🤔
Untitled.py
Untitled.py
Actually even in the ShellTask it does not work
Copy code
@task
def generate_command(select: str) -> str:
    return f"--select {select}"


with Flow(
    "model_on_demand",
) as dbt_flow:
    # Models to run on demand
    select = Parameter("select", required=True)
    shell_task(command=f"echo 'HELLO {generate_command(select=select)}'")
Ok I got it 👍
🚀 1
✨ 1
2 Views
Open in Slack
PreviousNext
Powered by

Prefect Community

Bring your towel and join one of the fastest growing data communities. Welcome to our second-generation open source orchestration platform, a completely rethought approach to dataflow automation.

Powered by