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# prefect-community
m
Matt Delacour
09/26/2022, 3:38 PMDo 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?
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✅ 1
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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
Bianca Hoch
09/26/2022, 4:21 PMHi 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
Matt Delacour
09/26/2022, 4:44 PMSo the solution is to
run()b
Bianca Hoch
09/26/2022, 9:11 PMAfter 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))with Flow(…)m
Matt Delacour
09/27/2022, 4:54 PMwill try that. Thank you
So it sounds like it works for
ShellTaskDbtShellTask Copy code
class DbtShellTask(ShellTask):
passUntitled.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 👍
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