Hi, I am refactoring my flow parameters and I encountered a slight problem when I compose two flows with a parameter with the same name:

ValueError: A task with the slug "limit" already exists in this flow.

I could come up with a plumbing hack like this:

flow = Flow(name)
        local_flow = build_local_flow()     # a function that returns a flow
        quetzal_flow = build_quetzal_flow() # idem

        # plumbing: both local and quetzal flows have a limit parameter
        limit_parameter = local_flow.get_tasks(name='limit')[0]
        other_parameter = quetzal_flow.get_tasks(name='limit')[0]
        for edge in quetzal_flow.edges:
            if edge.upstream_task == other_parameter:
                edge.upstream_task = limit_parameter
        quetzal_flow.tasks = set(t for t in quetzal_flow.tasks if t != other_parameter)
        flow.update(local_flow)
        flow.update(quetzal_flow)
        ...

which works, but it seems very hackish and far from elegant. Is there a cleaner alternative to this? (other than renaming the parameter, of course)

might be helpful if you provided the original code where you encountered the error

Here is a minimum working example of 2 flows and a composing flow that shows the problem:

import prefect

@prefect.task
def generate1(limit):
    return list(range(10))[:limit]


@prefect.task
def generate2(limit):
    return list(range(100, 1000))[:limit]


@prefect.task
def echo(x):
    print('Got', x)


with prefect.Flow('flow1') as flow1:
    limit1 = prefect.Parameter('limit')
    data1 = generate1(limit=limit1)
    echo.map(x=data1)

with prefect.Flow('flow2') as flow2:
    limit2 = prefect.Parameter('limit')
    data2 = generate2(limit=limit2)
    echo.map(x=data2)


flow3 = prefect.Flow('flow3')
flow3.update(flow1)
flow3.update(flow2)

Hey David - we’re aware of this frustration and trying to solve it in a cleaner way. It’s related to the fact that parameter names must be unique.

Ok! Do you have an issue/link/PIN I can follow to get updates?

we do now 🙂 https://github.com/PrefectHQ/prefect/issues/2501

That’s excellent