Fix explain() failing on UnaryFunction with multiple children

[Matt711]

Description

Oversight by me in #22984

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

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ℹ️ Recent review info

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Plan: Enterprise

Run ID: 3c09c4c0-39a3-462a-bf08-13fb68f5a9d2

📥 Commits

Reviewing files that changed from the base of the PR and between bf1cad5 and fa82e20.

📒 Files selected for processing (1)

• python/cudf_polars/cudf_polars/streaming/explain.py

🚧 Files skipped from review as they are similar to previous changes (1)

• python/cudf_polars/cudf_polars/streaming/explain.py

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved how unary expressions are displayed in streaming explanations, so functions with multiple inputs now appear in a clearer, standard format like name(arg1, arg2, ...).

Walkthrough

Modified _predicate_to_str in cudf_polars streaming explain output to format UnaryFunction expressions from all child arguments as a comma-separated call string.

Changes

Predicate String Formatting

Layer / File(s)	Summary
Multi-argument UnaryFunction rendering python/cudf_polars/cudf_polars/streaming/explain.py	_predicate_to_str's UnaryFunction case now builds name(arg1, arg2, ...) from all expr.children instead of formatting only a single child argument.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• rapidsai/cudf#22984: Modifies the same _predicate_to_str function in explain.py, extending predicate-to-string conversion logic used in plan node rendering.

Suggested reviewers

• vyasr

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main bug fix in the changeset.
Description check	✅ Passed	The description is related to the change and correctly references the fix and prior oversight.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[rjzamora]

Can you explain the motivation for this fix, like a CI failure? I'm interested to know what UnaryFunction consumes multiple children.

[Matt711]

/merge