Wait.on() in Python

[damccorm]

Python has no feature corresponding to Wait.on() in Java.

I see many python transforms use SideInput manually to workaround this, but it would be easy to make python pipelines if we have Wait.on() in python.

Imported from Jira BEAM-12878. Original Jira may contain additional context.
Reported by: baeminbo.

[SanjayPanda]

Hi @damccorm,

I came across from apache_beam.transforms.util import WaitOn in the Python SDK. Is this the same as what you were suggesting?

I'm working on a side input scenario where I need the side input to be ready before the main pipeline starts. Could you clarify if WaitOn is the right approach for this?

[damccorm]

Yes, it is the same, we should be able to close this issue.

I'm working on a side input scenario where I need the side input to be ready before the main pipeline starts. Could you clarify if WaitOn is the right approach for this?

If you're passing a side input in to the main PCollection, it should automatically get computed before that transform starts, so you shouldn't need anything special. WaitOn actually works by creating a side input relationship just like this.