TST: Add regression test for groupby().apply() external mutation #63126
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pandas-devGH-40673: Adds a test case to prevent regression of a bug where the internal object reused by apply() would corrupt externally stored DataFrames created with .copy(). This test verifies that store[0] and store[1] correctly contain independent copies of their respective groups.
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All CI checks passed, the pull request is ready for review but i don't see a button to request a reviewer. |
rhshadrach
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Nov 18, 2025
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rhshadrach
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Thanks for the PR - looking good!
| # The expected output in store dict | ||
| expected_out = {0: df[out_mask[0]], 1: df[out_mask[1]]} | ||
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| tm.assert_frame_equal(store[0], expected_out[0].drop("B", axis=1)) |
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Expected here can just be df.iloc[[0, 2], 1] I think.
| expected_out = {0: df[out_mask[0]], 1: df[out_mask[1]]} | ||
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| tm.assert_frame_equal(store[0], expected_out[0].drop("B", axis=1)) | ||
| tm.assert_frame_equal(store[1], expected_out[1].drop("B", axis=1)) |
| } | ||
| ) | ||
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| # Empty dict to hold the chunks |
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This comment and the ones below don't add anything that isn't already in the code. Can you remove them.
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GH-40673: Adds a test case to prevent regression of a bug where the internal object reused by apply() would corrupt externally stored DataFrames created with .copy(). This test verifies that store[0] and store[1] correctly contain independent copies of their respective groups.
doc/source/whatsnew/vX.X.X.rstfile if fixing a bug or adding a new feature.AGENTS.md.