Exposed source window to AssignContext in window_mapping_fn for side inputs

[alexmalao1]

Added source window to default_window_mapping_fn for side inputs. Existing window functions use timestamp to assign windows for side inputs, but custom windows not based on time would need to propagate the source window.

Addresses #36719

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[gemini-code-assist]

Summary of Changes

Hello @alexmalao1, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the flexibility of windowing for side inputs in Apache Beam by providing the full source window object to the AssignContext. This allows for more sophisticated and custom window assignment strategies that might rely on properties of the source window beyond just its maximum timestamp, addressing a limitation for non-timestamp-based windowing scenarios.

Highlights

• Enhanced Window Assignment for Side Inputs: The AssignContext within default_window_mapping_fn now explicitly exposes the source_window object, in addition to its max_timestamp.
• Support for Custom Windowing: This change enables custom window functions for side inputs that are not solely dependent on timestamps, allowing for more flexible window propagation logic.

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[github-actions]

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R: @damccorm for label python.

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[hjtran]

Nice find @alexmalao1. Could you include a test? Probably easiest to first put up a separate PR for adding the non-time-based custom window we've implemented and then creating a test using that

[damccorm]

Nice find @alexmalao1. Could you include a test? Probably easiest to first put up a separate PR for adding the non-time-based custom window we've implemented and then creating a test using that

+1 to adding a test, otherwise this LGTM though - thanks for the find

[github-actions]

Reminder, please take a look at this pr: @damccorm

[damccorm]

waiting on author

[github-actions]

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[github-actions]

This pull request has been closed due to lack of activity. If you think that is incorrect, or the pull request requires review, you can revive the PR at any time.

[alexmalao1]

Reopening review, added relevant unit test.

[github-actions]

Reminder, please take a look at this pr: @damccorm

[damccorm]

Looks like this is failing in CI with:

<testcase classname="apache_beam.transforms.sideinputs_test.SideInputsTest" name="test_default_window_mapping_fn_source_window" time="0.001">
<failure message="TypeError: Can't instantiate abstract class StringIDWindows with abstract method get_window_coder">self = <apache_beam.transforms.sideinputs_test.SideInputsTest testMethod=test_default_window_mapping_fn_source_window> def test_default_window_mapping_fn_source_window(self): """Test that the default window mapping function will propagate the source window when attempting to assign context. """ class StringIDWindow(window.BoundedWindow): """A window defined by an arbitrary string ID.""" def __init__(self, window_id: str): super().__init__(self._getTimestampFromProto()) self.id = window_id class StringIDWindows(window.NonMergingWindowFn): """ A windowing function that assigns each element a window with ID.""" def assign( self, assign_context: window.WindowFn.AssignContext ) -> Iterable[StringIDWindow]: if assign_context.element is None: return [assign_context.window] return [StringIDWindow(str(assign_context.element))] > mapping_fn = sideinputs.default_window_mapping_fn(StringIDWindows()) E TypeError: Can't instantiate abstract class StringIDWindows with abstract method get_window_coder apache_beam/transforms/sideinputs_test.py:513: TypeError</failure>
</testcase>

Could you please take a look?

[alexmalao1]

Added the required dummy _getTimestampFromProto and get_window_coder methods for the string id window examples.

Test should pass now.

[github-actions]

Reminder, please take a look at this pr: @damccorm

[damccorm]

waiting on author

[damccorm]

Would you mind adjusting this type hint? It looks like this is causing linting to fail: https://github.com/apache/beam/actions/runs/21918758108/job/63292969740?pr=36722

apache_beam/transforms/sideinputs_test.py:514: error: List item 0 has incompatible type "BoundedWindow | None"; expected "StringIDWindow"  [list-item]

[alexmalao1]

Updated to window.BoundedWindow

[damccorm]

Looks like linting checks are still failing - https://github.com/apache/beam/actions/runs/22365640103/job/64730757498?pr=36722 - could you please take a look?

You should be able to reproduce locally by running ./gradlew :pythonLintPreCommit

[github-actions]

Reminder, please take a look at this pr: @damccorm

[damccorm]

waiting on author