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BUG: replace with None cast unmatched same-dtype columns to object (GH#30512) - #1444

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BUG: replace with None cast unmatched same-dtype columns to object (GH#30512)#1444
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jbrockmendel/bug-30512

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@xirafa xirafa commented Oct 10, 2026 •
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Mirror of pandas-dev/pandas#71032. Runs the pandas test suite through dagz.

Summary by CodeRabbit

  • Bug Fixes
    • Fixed DataFrame.replace so replacing matching values with None no longer changes the dtype of other, unmatched columns.

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  • doc/source/whatsnew/v3.2.0.rst

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  • pandas/tests/frame/methods/test_replace.py

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📝 Walkthrough
📝 Walkthrough

Walkthrough

Block._replace_coerce now processes qualifying columns separately when replacing None. A regression test checks that unmatched columns retain their original dtypes, and the release notes describe the fix.

Changes

DataFrame.replace dtype handling

Layer / File(s) Summary
Per-column replacement and regression coverage
pandas/core/internals/blocks.py, pandas/tests/frame/methods/test_replace.py, doc/source/whatsnew/v3.2.0.rst		 When a replacement mask does not match every column in a qualifying block, replacement now splits the block and retries per column. The test covers inplace and non-inplace calls and checks the resulting values and dtypes. The release notes describe the case.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: jbrockmendel

Merge Risk: ⚪ Minimal · up to e64dc

This change stops DataFrame.replace from converting unmatched columns to object dtype when replacing with None. A regression test and release note are included. No merge-blocking risk was identified.

Pre-merge checks | Passed 4 | Failed 1

❌ Failed checks (1 warning)

Check name Status Explanation Resolution
Docstring Coverage Warning Docstring coverage is 25.00% 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. (1 skipped: 1… Write docstrings for the functions missing them to satisfy the coverage threshold.
✅ Passed checks (4 passed)
Check name Status Explanation
Description Check Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check Passed The title clearly identifies the main bug fix: replacing with None no longer casts unmatched same-dtype columns to object. It is concise and includes the related issue number.
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.
Full details: Docstring Coverage

Explanation

Docstring coverage is 25.00% 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. (1 skipped: 1 unsupported.)

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@xirafa
xirafa force-pushed the main branch 11 times, most recently from c85b9f5 to a5a62b9 Compare October 11, 2026 16:44
@jbrockmendel @claude
BUG: replace with None cast unmatched same-dtype columns to object (G…
8c4ec27 
…H#30512)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
@xirafa
xirafa force-pushed the main branch 2 times, most recently from 1c2aae1 to 7edc0f5 Compare October 11, 2026 19:32
@xirafa
xirafa force-pushed the jbrockmendel/bug-30512 branch from e64dcba to 8c4ec27 Compare October 11, 2026 20:51
@xirafa
xirafa force-pushed the main branch 14 times, most recently from 9e87d20 to aaf445d Compare October 13, 2026 03:34
@xirafa
xirafa force-pushed the main branch 30 times, most recently from ef1f5bc to 3d4a7fc Compare October 16, 2026 21:07
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2 participants

@xirafa @jbrockmendel