Add `output` property to MappedOperator #25604

josh-fell · 2022-08-08T12:50:09Z

Currently the output property of operators is only available to unmapped "classic" operators. There can be use cases in which XComs from a set of mapped tasks need to be consumed by a downstream task. Of course, accessing these mapped-task XComs can be done with the typical Jinja template, but having the convenience of using the output property would be a "quality of life" improvement for DAG authors (especially since task dependencies would then be automatically implemented too).

Rather than adding the property to MappedOperator and have this property definition exist in two locations (along with BaseOperator), I opted to add this to AbstractOperator given all tasks have an output even if that output is empty and both BaseOperator and MappedOperator share the AbstractOperator implementation. If there a higher-level reason to have two instances of the property definition, I'm happy to oblige.

This PR adds the output property to MappedOperator and includes a return type annotation for XComArg. Additionally, until a more appropriate API implementation of accessing a different XCom key from output other than "return_value" is decided, the example DAGs and system tests using this API have been updated to explicitly use XComArg(operator, key=...) instead.

~~TODO:~~
~~Add docs demonstrating the use of this property with mapped tasks.~~ May be handled in #25617

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uranusjr · 2022-08-09T09:06:44Z

TIL about output. Maybe we should promote it more instead of telling the user to import XComArg directly!

potiuk · 2022-08-09T10:37:47Z

TIL about output. Maybe we should promote it more instead of telling the user to import XComArg directly!

Yeah. Promoting more the TaskFlow and outputs is something we should really do.
I think we should start with changing our documentation with reversing the sequence and generally putting a different emphasis:

"The right way of wriging tasks (Task Flow and Hooks)" and
"The Old and legacy way of doing things (the operators).

josh-fell · 2022-08-09T16:57:13Z

Yeah slowly trying to change the docs around -- at least to promote TaskFlow API instead of the classic operators. I logged #25319 to update code snippets throughout.

uranusjr · 2022-08-11T05:29:57Z

Hmm, the static check failures raise a point for discussion. XComArg has an (unfortunate) API design xcom_arg[key] that can be used to pull an XCom under a different key, but I’m not sure I like it being used with output. task.output["foo"] feel to me more like accessing a dict, not pulling another XCom. The API design can be discussed/changed later, but here I think we should decide whether that is a usage we want to encourage or not (personally I’m against).

josh-fell · 2022-08-15T18:35:44Z

Hmm, the static check failures raise a point for discussion. XComArg has an (unfortunate) API design xcom_arg[key] that can be used to pull an XCom under a different key, but I’m not sure I like it being used with output. task.output["foo"] feel to me more like accessing a dict, not pulling another XCom. The API design can be discussed/changed later, but here I think we should decide whether that is a usage we want to encourage or not (personally I’m against).

I have the same icky feeling with that current syntax as well. It's also not functionally equivalent to the classic ti.xcom_pull(task_id=..., key=...)["some_item"] which I opened an issue about last year. There was some discussion on what to change the API to, but there was also a little of "that ship has sailed" vibe as well. Since this is coming up again, it's probably time to raise a discussion about it on the dev list.

In the meantime, WDYT about allowing operator.output(key=...)? It's functionally possible to pass in a key arg to XComArg already, the syntax isn't too bad, and has a less confusing API than the current one. I'm happy to work on this if it's a happy middle ground.

josh-fell · 2022-08-15T18:51:06Z

Side note, the example DAGs were all updated as best as possible to follow the new TaskFlow syntax (see #10285). I have no problem updating these again.

uranusjr · 2022-08-16T05:00:48Z

WDYT about allowing operator.output(key=...)?

Doesn’t this conflict with using op.output as a property though? It’s possible but quite difficult to implement output as both an XComArg and callable. Maybe op.get_xcom(key=...) (or something like that) would be easier.

The general direction feels like a good idea to me though. I also plan to add some mechanism in #25661 to avoid exposing the bracket syntax:

Keep XComArg(...) and the return value of @task work as-is (so any existing code depending on the bracket syntax continues to work)
Introduce a new XComArg class that does not provide the bracket syntax, and use that in output and get_xcom() etc.

Does this sound like a good plan?

josh-fell · 2022-08-23T04:09:50Z

The general direction feels like a good idea to me though. I also plan to add some mechanism in #25661 to avoid exposing the bracket syntax:

Keep XComArg(...) and the return value of @task work as-is (so any existing code depending on the bracket syntax continues to work)

Introduce a new XComArg class that does not provide the bracket syntax, and use that in output and get_xcom() etc.

Does this sound like a good plan?

Sounds like a good one to me.

uranusjr · 2022-08-23T20:59:10Z

airflow/example_dags/example_xcom.py

+        f'echo "The xcom pushed manually is {XComArg(bash_push, key="manually_pushed_value")}" && '
+        f'echo "The returned_value xcom is {XComArg(bash_push)}" && '


The latter one can still use output although using XComArg for both is probably more consistent…?

Yeah, it might be better to be consistent. There are some other places I need to clean that up to use XComArg() throughout rather than .output for now. Is that cool?

Although maybe as long as each file is consistent that's fine. .output is still a valid and useful API. I don't think we want to rip it out of all of the examples.

uranusjr · 2022-08-23T21:01:14Z

airflow/providers/amazon/aws/example_dags/example_ecs.py

@@ -99,18 +100,20 @@
    )
    # [END howto_operator_ecs_register_task_definition]

+    registered_task_definition = cast(str, register_task.output)


It’s probably a good idea to add a Mapy plugin for this… I’ll look into it after this is merged.

Great! I was going to ask if there was a better way than doing all of these cast() calls. Had to be something we could do with mypy specifically.

josh-fell · 2022-08-26T15:49:29Z

🤞 on CI. I think I finally got everything and new stuff.

josh-fell · 2022-08-26T19:33:40Z

Nice check to make sure providers would still be compatible with Airflow 2.2! Caught some import issues.

potiuk · 2022-08-26T20:20:11Z

Nice check to make sure providers would still be compatible with Airflow 2.2! Caught some import issues.

:D :D :D -> sometimes those are REALLY useful (even if annoying).

This makes things easier for type checkers.

Importing `XComArg` directly from the `airflow` namespace wasn't available until 2.3. Providers only have a minimum req of 2.2. The previous import method would have implicitly required a minimum Airflow 2.3 version.

# Description ## What is the current behavior?  The output was implemented in 2.4.0 according to the release notes (see [here](https://airflow.apache.org/docs/apache-airflow/stable/release_notes.html#id13)) Add output property to MappedOperator apache/airflow#25604  closes: #1359 ## What is the new behavior?  - Catch exception for airflow version < 2.4.0 and use `XComArg(...)` instead. ## Does this introduce a breaking change? No ### Checklist - [x] Created tests which fail without the change (if possible) - [x] Extended the README / documentation, if necessary Co-authored-by: Kaxil Naik <kaxilnaik@gmail.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

# Description ## What is the current behavior?  The output was implemented in 2.4.0 according to the release notes (see [here](https://airflow.apache.org/docs/apache-airflow/stable/release_notes.html#id13)) Add output property to MappedOperator apache/airflow#25604  closes: #1359 ## What is the new behavior?  - Catch exception for airflow version < 2.4.0 and use `XComArg(...)` instead. ## Does this introduce a breaking change? No ### Checklist - [x] Created tests which fail without the change (if possible) - [x] Extended the README / documentation, if necessary Co-authored-by: Kaxil Naik <kaxilnaik@gmail.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> (cherry picked from commit 0f5ff62)

uranusjr approved these changes Aug 9, 2022

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uranusjr mentioned this pull request Aug 9, 2022

Promote Operator.output more #25617

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josh-fell marked this pull request as ready for review August 9, 2022 16:35

josh-fell force-pushed the mappedop-output-prop branch from c5c4031 to 793ace8 Compare August 9, 2022 16:59

kaxil approved these changes Aug 12, 2022

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josh-fell force-pushed the mappedop-output-prop branch from b14dffc to 2fc9d41 Compare August 23, 2022 04:02

josh-fell requested a review from turbaszek as a code owner August 23, 2022 04:02

josh-fell changed the title ~~Add output property to common operator implementation~~ Add output property to MappedOperator Aug 23, 2022

josh-fell force-pushed the mappedop-output-prop branch 2 times, most recently from f0db611 to ea3c62f Compare August 23, 2022 20:56

uranusjr reviewed Aug 23, 2022

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uranusjr approved these changes Aug 23, 2022

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uranusjr mentioned this pull request Aug 23, 2022

Develop Mypy plugin to type-check XComArg passed to a template_field #25922

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josh-fell force-pushed the mappedop-output-prop branch from ea3c62f to 5219511 Compare August 26, 2022 15:37

josh-fell and others added 4 commits August 26, 2022 22:08

Add output property to common operator implementation

14f6d05

Move 'output' to operator implementations

6966ef7

This makes things easier for type checkers.

Fix mypy errors in example DAGs and system tests

43621d3

fixup! Fix mypy errors in example DAGs and system tests

f3fa398

josh-fell added 2 commits August 26, 2022 22:08

Make XComArg import compatible with Airflow 2.2

6b85630

Importing `XComArg` directly from the `airflow` namespace wasn't available until 2.3. Providers only have a minimum req of 2.2. The previous import method would have implicitly required a minimum Airflow 2.3 version.

Resolve conflicts

2848743

josh-fell force-pushed the mappedop-output-prop branch from c144471 to 2848743 Compare August 27, 2022 02:09

uranusjr merged commit 1ed0146 into apache:main Aug 28, 2022

uranusjr mentioned this pull request Aug 28, 2022

Hook into Mypy to get rid of those cast() #26023

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josh-fell deleted the mappedop-output-prop branch August 28, 2022 18:39

ephraimbuddy added the type:new-feature Changelog: New Features label Sep 13, 2022

ephraimbuddy added this to the Airflow 2.4.0 milestone Sep 14, 2022

This was referenced Sep 28, 2022

Status of testing Providers that were prepared on September 28, 2022 #26752

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Status of testing Providers that were prepared on October 04, 2022 #26864

Closed

feluelle mentioned this pull request Dec 6, 2022

Clean up operator failing astronomer/astro-sdk#1359

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sunank200 mentioned this pull request Dec 7, 2022

Fix output property missing for airflow version < 2.4.0 astronomer/astro-sdk#1385

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Add `output` property to MappedOperator #25604

Add `output` property to MappedOperator #25604

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potiuk commented Aug 26, 2022

		f'echo "The xcom pushed manually is {XComArg(bash_push, key="manually_pushed_value")}" && '
		f'echo "The returned_value xcom is {XComArg(bash_push)}" && '

Add output property to MappedOperator #25604

Add output property to MappedOperator #25604

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Add `output` property to MappedOperator #25604

Add `output` property to MappedOperator #25604

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