Sandbox::https://togithub.com/apache/airflow/pull/18471

eladkal · 2021-09-23T14:27:52Z

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uranusjr · 2021-09-23T14:39:38Z

Instead of explicitly forbidding this, would it be reasonable to handle the None case and skip all the downstreams instead?

eladkal · 2021-09-23T14:41:03Z

Instead of explicitly forbidding this, would it be reasonable to handle the None case and skip all the downstreams instead?

When would None be desired?

josh-fell · 2021-09-23T15:06:03Z

Instead of explicitly forbidding this, would it be reasonable to handle the None case and skip all the downstreams instead?

When would None be desired?

I could understand users may not want the DAG to fail outright if the branching section is not critical path like with some feature engineering use cases I've seen. It may be more intuitive to not have to create an empty branch to simply continue with the pipeline if an output doesn't need to be tracked. An edge case for sure with an obvious workaround.

Could this be a configurable mode: fail or skip if no branches found?

eladkal · 2021-09-23T15:20:10Z

I could understand users may not want the DAG to fail outright if the branching section is not critical path like with some feature engineering use cases I've seen. It may be more intuitive to not have to create an empty branch to simply continue with the pipeline if an output doesn't need to be tracked. An edge case for sure with an obvious workaround.

Could this be a configurable mode: fail or skip if no branches found?

This sounds more like a wrong usage of branching. For conditional junctions we have ShortCircuitOperator
but i'm OK with @uranusjr suggestion if this is prefered.

josh-fell · 2021-09-23T16:01:20Z

Perhaps but the ShortCircuitOperator can be redundant here if we're skipping downstream tasks with this operator now. Seconded on @uranusjr's suggestion as well FWIW.

MatrixManAtYrService · 2021-09-23T16:01:40Z

I had the same thought as @uranusjr, skipping all downstream tasks seems like an obvious way to interpret None to me, like an if statement with no else.

I'm not gonna fight for it though. Scope creep is real and I'll be happy enough to have a better error.

eladkal · 2021-09-23T16:41:55Z

@uranusjr correct me if I'm wrong but this requires rewriting skip_all_except
The way I see it I can't just blindly skip all downstream tasks as unlike ShortCircuitOperator branching does respect trigger rules so I need to skip all downstream tasks until a join/junction task is found.
Since my input is None we need to search if such junction exists.
So I need to set difference between two cases:

If I have a case of:

        # branch  ----->  task2
        #   \           
        #    \        
        #       task1

Then I need to execute skip
but If I have a case like:

        # branch  ----->  task2   <----- task3
        #   \           
        #    \        
        #       task1

Then I need to run skip_all_except(context['ti'],['task2]) because task2 may still run depends on its trigger_rule.

ashb · 2021-09-23T18:54:47Z

If you want to skip everything you can raise AirflowSkipException I think. (that would have a slightly different behaviour of also skipping the branch op itself, unless we caught that in this op and turned it in to skip all downstream)

That's all a separate pr/feature though

eladkal · 2021-09-24T07:57:44Z

If you want to skip everything you can raise AirflowSkipException I think. (that would have a slightly different behaviour of also skipping the branch op itself, unless we caught that in this op and turned it in to skip all downstream)

So this is a possible route. We will need to keep the change in SkipMixin itself to avoid changing all the branch operators.

That's all a separate pr/feature though

I agree. This PR is just replacing the error message to a more meaningful one. There is no change in functionality here.
I'll work on trying to solve the issue from the root for a future PR.

uranusjr · 2021-09-24T09:31:49Z

Kind of wondering whether we should check for all non-str values. Or even check the value is a valid task ID? Something like…

if isinstance(branch, str): branches = [branch] try: branches = list(branch) # Check iterability. except TypeError: raise AirflowException("Branch callable must return either a task ID or a list of IDs") valid_task_ids = set(context["dag"].task_ids) if not any(b in valid_task_ids for b in branches): raise AirflowException("Branch callable must return at least one task ID to follow")

yeah this is something I had in mind - added it in last commit
In general this is something we should have in skipmixin as it's logic shared by all branch operators.

github-actions · 2021-09-24T09:33:41Z

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

potiuk · 2021-09-25T11:32:56Z

    def execute(self, context: Dict):
        branch = super().execute(context)
+        # TODO: The logic should be moved to SkipMixin to be available to all branch operators.
+        if isinstance(branch, str):


Should we also change SkipMixin while we are changing it (or will it be a separate PR) ? (per the comment above)

Seperate PR.
I will work on it. We want also to change the functionality so it will accept None and skip all downstream tasks (untill a junction/join task).

edwardwang888 · 2021-09-29T19:36:57Z

+        invalid_task_ids = branches - valid_task_ids
+        if invalid_task_ids:
+            raise AirflowException(
+                f"Branch callable must valid task_ids. Invalid tasks found: {invalid_task_ids}"


@eladkal Did you mean something like
Branch callable must *return* valid task_ids?

Ah yeah. Ill raise a PR to fix it.

boring-cyborg Bot added the area:core-operators label Sep 23, 2021

eladkal requested a review from ashb September 23, 2021 14:28

MatrixManAtYrService mentioned this pull request Sep 23, 2021

BranchPythonOperator intermittently fails to find its downstream task ids #18454

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uranusjr reviewed Sep 24, 2021

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uranusjr approved these changes Sep 24, 2021

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github-actions Bot added the full tests needed We need to run full set of tests for this PR to merge label Sep 24, 2021

eladkal added 2 commits September 25, 2021 00:23

Improve error message for BranchPythonOperator when no task_id to follow

111f879

fixes

20a4f47

eladkal force-pushed the python branch from 46de2d7 to 20a4f47 Compare September 24, 2021 21:24

uranusjr reviewed Sep 24, 2021

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Comment thread airflow/operators/python.py Resolved

change if

ac002b9

eladkal added this to the Airflow 2.2.0 milestone Sep 24, 2021

potiuk reviewed Sep 25, 2021

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potiuk approved these changes Sep 25, 2021

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eladkal merged commit c1578fb into apache:main Sep 25, 2021

eladkal deleted the python branch September 25, 2021 17:55

edwardwang888 reviewed Sep 29, 2021

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eladkal mentioned this pull request Oct 29, 2021

none_failed_min_one_success trigger rule not working with BranchPythonOperator in certain cases. #19222

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eladkal mentioned this pull request Dec 20, 2021

Allow to except_skip None on BranchPythonOperator #20411

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eladkal mentioned this pull request Oct 31, 2022

Improve error message when branched task_id does not exist #27409

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eladkal commented Sep 23, 2021

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