Adapt numerical base transformers to narwhals-returning check_X - #1022
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solegalli merged 1 commit intoAug 30, 2026
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Since #1019, check_X / check_X_y return a narwhals DataFrame instead of the native frame. BaseNumericalTransformer._fit_setup / ._check_transform_input_and_state and FitFromDictMixin._fit_from_dict rebind `X = check_X(X)` and then pass that frame to find_numerical_variables, check_numerical_variables, _check_contains_na and _check_contains_inf. Those helpers branch on nwd.is_pandas_dataframe() internally. Handed a narwhals frame they take the non-pandas path and emit a UserWarning per call ("You passed a narwhals.dataframe.DataFrame to is_pandas_dataframe") - a single LogTransformer.fit_transform on pandas raised 5 such warnings - while the pandas fast paths are silently skipped. check_X is pure validation (no copy, no reshape), so the fix is to stop rebinding X and keep passing the helpers the native input, exactly as before #1019. The transformation classes themselves need no changes (they are already backend-agnostic: nw.from_native(X) on whatever the base returns). This also restores the pre-#1019 baseline for the other consumers of these bases: test_scaling 19/0 (was 14 failing), test_discretisation 5 failing (was 23). No test changes; mypy and flake8 clean. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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update classes to narwhals return from check_x