what does this error implies:

TypeError: `fn` must be callable

I’m calling a task inside a With Flow statement, and the Task should return me a list of strings

Hi @Chu, what is the output of

prefect version

? I suspect you're writing prefect 1.0 code using

prefect>=2.0

it’s 1.2.2

okay - is there anything else you need help with?

What are the Parameter() call returns, a JSON object?, Is there a method I can deserialize it to its original input, for example:

params = Parameter("ids", default=['a','b','c'])

like to deserialize

params

to [‘a’,‘b’,‘c’]

in Prefect 1.0, the

Parameter

object is a special type of task, so within the

with Flow(...) as flow:

block (called the flow context) the return of your task will be of type

prefect.tasks.core.function.FunctionTask

and you cannot [sic] access the true value (a list in your case) in the flow context however, when you pass this

Parameter

to a downstream task, you can treat it as a list like you'd expect, for example you could have

@task(log_stdout=True)
def my_downstream_task(my_params: List[str]):
    print(type(my_params))
    print(my_params)

    # do other things with your params

with Flow('my flow') as flow:
    params = Parameter("ids", default=['a','b','c'])

    my_task_result = my_downstream_task(params)
    
if __name__ == "__main__":
    flow.run()

I think I can get it by calling

params.default

oh, wow I didn't know that was there - nice find!

haha! I found it in source code, it’s an attribute of that Class when instantiated https://github.com/PrefectHQ/prefect/blob/1.x/src/prefect/core/parameter.py#:~:text=%22%22%22-,def%20__init__(,)%3A,-if%20required%20is

that's awesome - thanks for teaching me something today! I would encourage you to check out prefect 2.0 at some point, since you can interact directly with task results in all contexts / scopes of your code and you can arbitrarily nest flow calls - here are some docs on subflows in 2.0 if you're interested!

For sure, we are in a transition to Prefect 2.0, and certain Prefect 2.0 will do better than 1.0, but still glad we find some workaround in 1.0 (to make it work) and hope this may help others in the community