[raams95]

Fixes #19154

When beam.Partition is applied to a list instead of a PCollection, the result can't be indexed with an int:

>>> partitions = [0, 1, 2, 3, 4] | beam.Partition(lambda e, n: e % n, 2)
>>> partitions[0]
KeyError: "Tag 0 is not a defined output tag of <DoOutputsTuple main_tag=None tags=('0', '1') transform=<ParDo(PTransform) label=[ParDo(ApplyPartitionFnFn)]>>."

Inside a pipeline partitions[0] works, because DoOutputsTuple.__getitem__ converts int tags to strings so that partitions can be looked up with the same ints the partition function returns. The result of applying a transform to a list is a _MaterializedDoOutputsTuple, whose __getitem__ overrides that method without the conversion, so only partitions['0'] works there.

This change does the same int to string conversion in _MaterializedDoOutputsTuple.__getitem__.

I added test_partition_applied_to_list to ptransform_test.py. It fails with the KeyError above before the change and passes after it.

Testing:

• pytest apache_beam/transforms/ptransform_test.py apache_beam/pvalue_test.py apache_beam/pipeline_test.py
• yapf --diff and ruff check on the changed files

---

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[github-actions]

📋 Review Summary

This PR resolves #19154 by converting integer tags to strings in _MaterializedDoOutputsTuple.__getitem__, matching the existing behavior of DoOutputsTuple.__getitem__. The implementation is clean, minimal, and properly covered by a unit test.

🔍 General Feedback

• The change accurately aligns eager materialization output indexing with deferred pipeline DoOutputsTuple indexing.
• The unit test in ptransform_test.py and the CHANGES.md entry are well-structured and complete.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.01%. Comparing base (76f6e6d) to head (ee413ab).
⚠️ Report is 242 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40681       +/-   ##
=============================================
+ Coverage     56.16%   80.01%   +23.84%     
=============================================
  Files          1124      490      -634     
  Lines        178336    82813    -95523     
  Branches       1489        0     -1489     
=============================================
- Hits         100170    66261    -33909     
+ Misses        75645    16552    -59093     
+ Partials       2521        0     -2521     

Flag	Coverage Δ
go	?
java	?
python	80.01% <100.00%> (+0.45%)	⬆️

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[github-actions]

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