Fix type checking failure with Python 3.10+ union pipe syntax (int | None)

[junaiddshaukat]

Summary

Fixes #36592

Using Python 3.10+ pipe operator union types (e.g. int | None) in function type hints causes TypeError: issubclass() arg 1 must be a class when Beam performs type checking.

# This was crashing:
def func(x: int, y: int | None = None):
    return x

with beam.Pipeline() as p:
    (p | beam.Create([1]) | beam.Map(func))
# TypeError: issubclass() arg 1 must be a class

Root Cause

The normalize() function in typehints.py did not handle types.UnionType (Python 3.10+ pipe union syntax). On Python 3.10–3.13, int | None creates a types.UnionType whose module is not 'typing' and has no origin, so it passed through normalize() unchanged. This caused is_consistent_with() to fall through to issubclass() with a non-class argument.

Fix

Added a types.UnionType check in normalize() that routes pipe union types through convert_to_beam_type(), which already handles the conversion to Beam's UnionConstraint.

Tests Added

test_hint_helper_pipe_union — verifies is_consistent_with() works with pipe union types
test_normalize_pipe_union — verifies normalize() converts types.UnionType to UnionConstraint

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[gemini-code-assist]

Summary of Changes

Hello @junaiddshaukat, 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 addresses a TypeError in Apache Beam's type checking that occurred when using Python 3.10+ union pipe syntax (e.g., int | None). The fix involves updating the normalize function to correctly process these new union types, ensuring compatibility and preventing runtime errors. New tests have been added to validate the correct handling of these type hints.

Highlights

• Problem Addressed: Resolved a TypeError occurring in Apache Beam's type checking when Python 3.10+ union pipe syntax (e.g., int | None) was used in function type hints.
• Root Cause Identified: The normalize() function in typehints.py did not recognize types.UnionType, leading to incorrect handling and subsequent TypeError when issubclass() was called with a non-class argument.
• Solution Implemented: Modified the normalize() function to include a check for types.UnionType and route these types through native_type_compatibility.convert_to_beam_type(), which correctly converts them to Beam's UnionConstraint.
• New Tests Added: Introduced test_hint_helper_pipe_union to verify is_consistent_with() works with pipe union types, and test_normalize_pipe_union to confirm normalize() correctly converts types.UnionType to UnionConstraint.

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Changelog

• sdks/python/apache_beam/typehints/typehints.py
  • Added a new elif condition in the normalize function to detect types.UnionType instances.
  • Integrated native_type_compatibility.convert_to_beam_type to handle the conversion of types.UnionType to Beam's internal type representation.
  • Included a fallback to Any if convert_to_beam_type returns the original type.
• sdks/python/apache_beam/typehints/typehints_test.py
  • Introduced test_hint_helper_pipe_union to assert that is_consistent_with correctly evaluates Python 3.10+ pipe union types against various other types.
  • Added test_normalize_pipe_union to verify that the normalize function successfully transforms types.UnionType objects into typehints.UnionConstraint instances.

Activity

• No specific activity (comments, reviews, etc.) was provided in the context beyond the initial pull request description.

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[github-actions]

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[junaiddshaukat]

assign set of reviewers

[github-actions]

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R: @damccorm for label python.

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[damccorm]

@jrmccluskey could you please take a look?

[jrmccluskey]

Having the extra test coverage is nice but it's worth noting that this suite passes even without the changes to typehints.py

[jrmccluskey]

Adding the extra conditional here and repeating the same code as the other categories that get converted is clunky. Now that the list of checks is reasonably long, it may be worth splitting them out into a helper function for readability; otherwise, isinstance(x, types.UnionType) should be worked into the existing elif statement.

[junaiddshaukat]

@jrmccluskey Thanks for the review! I've addressed all your feedback:

1. Merged isinstance(x, types.UnionType) into the existing elif — no more duplicated code block, it now extends the existing condition.
2. Removed the GH issue link comments from both test methods.

Formatting verified clean with yapf==0.43.0. Ready for another look!

[jrmccluskey]

LGTM, thanks! The test failures are unrelated.