Fix line numbers reported by python -m cudf.pandas --line-profile

[Dev-next-gen]

Description

While reading how python -m cudf.pandas --line-profile builds its instrumented copy of a script, I noticed that profile() in cudf/pandas/__main__.py reads the script with readlines(), which keeps each line's trailing newline, and lines_with_profiling then joins those lines with "\n". Every source line ends up followed by an empty line in the instrumented file, and since the injected code only shifts line numbers back by 2, the per-line table reports line 2k-1 for line k. The %%cudf.pandas.line_profile cell magic is not affected because it passes cell.split("\n").

The fix reads the script with f.read().split("\n"), the same way the cell magic splits a cell. Nothing else changes: lines_with_profiling and the cell magic are untouched.

I don't have an NVIDIA GPU, so I checked it by loading the real profiler.py and __main__.py from the checkout, with only cudf.pandas/__init__ and fast_slow_proxy stubbed out, and running profile(False, True, script) plus _run_instrumented_as_main on a four-line script (x = 1, y = 2, z = 3, print(x + y + z)). The script's output is the same in both cases; the table rows are:

before (main at 4868806bb4)      after
line 1: x = 1                    line 1: x = 1
line 3: y = 2                    line 2: y = 2
line 5: z = 3                    line 3: z = 3
line 7: print(x + y + z)         line 4: print(x + y + z)

I added test_run_cudf_pandas_line_profile_reports_script_line_numbers next to the existing --line-profile test in test_main.py. It parses the line numbers out of the table with the same regex my check used, but I could not run the test itself here since it goes through python -m cudf.pandas, which needs a GPU.

Checklist

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

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📝 Summary

Summary by CodeRabbit

• Bug Fixes

  • Fixed line profiling to report accurate line numbers from the original script.

• Tests

  • Added regression coverage to verify correct line-number reporting when using line profiling.

Walkthrough

The line-profile source reader now splits scripts on newline separators before instrumentation. A regression test verifies that profiling output reports the original line numbers for a four-line script.

Changes

Line-profile input handling

Layer / File(s)	Summary
Input splitting and line-number validation python/cudf/cudf/pandas/__main__.py, python/cudf/cudf_pandas_tests/test_main.py	The line-profile path splits script input before instrumentation. The regression test parses profiling output and checks line numbers 1 through 4.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix · Severity of issue fixed: Low

Merge Risk: 🔵 Low · up to 4b826

The line-profile behavior is tested, but the required benchmark is missing; the change is otherwise suitable for merge with this follow-up.

🚥 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	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 identifies the primary change: correcting line numbers reported by python -m cudf.pandas --line-profile.
Description check	✅ Passed	The description directly explains the line-numbering bug, the script-reading fix, the unchanged cell magic, and the added regression test.
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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Actionable comments posted: 1

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Inline comments:
In `@python/cudf/cudf_pandas_tests/test_main.py`:
- Line 63: Add a unit benchmark alongside
test_run_cudf_pandas_line_profile_reports_script_line_numbers that measures
profiling setup using a representative script and temporary path. Reuse the
existing test setup and profiling input path so the benchmark covers the same
behavior without changing the regression test.

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📥 Commits

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📒 Files selected for processing (2)

• python/cudf/cudf/pandas/__main__.py
• python/cudf/cudf_pandas_tests/test_main.py

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[Dev-next-gen]

One note on CI: the Label Checker is red because the PR is missing a category label and a breaking/non-breaking label. It currently carries Python and cudf.pandas. I tried to add bug and non-breaking myself and the API returns 403 — those labels need someone with write access on the repo.

The rest of the checks that can run are green; the test jobs are still waiting on the copy-pr-bot vetting step.