Fix ValueError on read-only arrays in BaseSLearner.predict()#878
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jeongyoonlee merged 2 commits intouber:masterfrom Feb 23, 2026
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Learners like CatBoost set flags.writeable=False on arrays passed to predict(), causing the subsequent in-place mutation (X_new[:, 0] = 1) to raise ValueError. Build separate control and treatment arrays instead of mutating in place.
Adds ReadOnlyLinearRegression wrapper that simulates CatBoost's behavior of setting flags.writeable=False on arrays after fit/predict. Verifies BaseSLearner.predict() succeeds without ValueError.
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Changes
Fixes #856.
Learners like CatBoost set
flags.writeable=Falseon arrays passed topredict()as a side effect. InBaseSLearner.predict()andBaseSClassifier.predict(), the code was mutatingX_newin place (X_new[:, 0] = 1) after the learner had already made it read-only, raisingValueError: assignment destination is read-only.This PR builds separate control and treatment arrays instead of mutating in place.
Tests
Added
test_BaseSLearner_predict_with_readonly_arrayswith aReadOnlyLinearRegressionwrapper that simulates CatBoost's behavior. All 27 existing meta-learner tests continue to pass.References
ValueError: assignment destination is read-onlyinBaseSLearner.predictwithcatboostandpolars#856