A Flow s parameters need to be passed to at least one task s

Question

A Flow s parameters need to be passed to at least one task s run function or error would be raised right from prefect import task Flow Parameter from prefect core task import Task class print plus one Task def init self x super init self x = x def run self print self x + 1 with Flow Parameterized Flow as flow x = Parameter x print plus one x flow run parameters=dict x=1 prints 2 flow run parameters=dict x=100 prints 101 ValueError Flow run received the following unexpected parameters x

Chris White · Answer

Hi < Gary Liao> this is a very common confusion the Parameter needs to be added to the Flow initializing a Parameter within a Flow context is a red herring you could just as easily initialize it outside of a Flow context and the Flow would never know it existed

Chris White · Answer

in order to add it to the flow you need to explicitly call a method such as `flow add task x ` use the parameter in a downstream task

Chris White · Answer

this is discussed in greater detail here <https docs prefect io core tutorials task guide html adding tasks to flows>

Chris White · Answer

also just as an FYI if you want to format your code in slack you can surround it with triple backticks ``` on newlines before and after the code block

Gary Liao · Answer

Thnanks for tips new to slack I did use the parameter in a downstream task but in the init function not in the run function

Chris White · Answer

No worries Initializing a Task is not something Prefect tracks as a dependency if you really want a Prefect Parameter to be the `x` attribute of your Task then you can do that but Prefect won t treat that as a dependency

Gary Liao · Answer

Thank you~ Your teams are awesome

Chris White · Answer

Thanks < Gary Liao> anytime always glad to help