Hi guys I have next computational graph It was easy to imple

Question

Hi guys I have next computational graph It was easy to implement using functional API Usually I want to run all five tasks But sometimes I want to run only upper branch `t1` `t3` or lower branch `t1` `t4` and `t5` Is it possible to do without rewriting code from ```with Flow flow as flow r1 = t1 r2 = t2 r1 r3 = t3 r2 r4 = t1 r1 r5 = t5 r4 ``` into ```def upper branch r1 = t1 r2 = t2 r1 r3 = t3 r2 def lower branch r1 = t1 r4 = t4 r1 r5 = t5 r2 with Flow flow as flow if do upper or do both upper branch if do lower or do both lower branch ```

trapped · Answer

I believe you can use `prefect tasks control flow conditional ifelse` <https docs prefect io core task library control flow html control flow>

Jeremiah · Answer

Yup this is exactly what the ifelse is for You can use a Parameter to control which branch to execute

Nikita Vostretsov · Answer

From code readability point view this variant is not better then using separate functions and python s `if` I was thinking about something like ```with Flow flow as flow r1 = t1 r2 = t2 r1 r3 = t3 r2 r4 = t1 r1 r5 = t5 r4 targets = if do upper or do both targets append r3 if do upper or do both targets append r5 flow run targets=targets ```

Jeremiah · Answer

< Nikita Vostretsov> Python s `if` is not available inside a flow since it is executed at build time Prefect s `ifelse` is executed at run time and can therefore depend on information available when the flow runs In your example the flow actually runs both branches no matter what as you have no runtime control flow implemented The only thing changing is the input to your `targets` keyword argument which is presumably a Parameter not shown here

Jeremiah · Answer

The pattern you d like to implement is what `ifelse` is intended for you want to make a decision at runtime about which branch to execute If on the other hand you know which branch you want to run AND you don t mind rebuilding your flow each time which might be fine for your purposes then you could use a Python `if` to control which tasks you add to the flow However if you want a single flow with multiple branches you ll need a Prefect `ifelse`