FIX Fixes transform wrappig in _SetOutputMixin (scikit-learn#25295)

thomasjpfan · web-flow · commit a0a6ea744f35 · 2023-01-10T17:47:11.000+01:00
Fixes scikit-learn#25293
diff --git a/doc/whats_new/v1.2.rst b/doc/whats_new/v1.2.rst
@@ -19,6 +19,9 @@ Changelog
   certain estimators to be pickled when using Python 3.11. :pr:`25188` by
   :user:`Benjamin Bossan <BenjaminBossan>`.
 
+- |Fix| Inheriting from :class:`base.TransformerMixin` will only wrap the `transform`
+  method if the class defines `transform` itself. :pr:`25295` by `Thomas Fan`_.
+
 :mod:`sklearn.linear_model`
 ...........................
 
diff --git a/sklearn/utils/_set_output.py b/sklearn/utils/_set_output.py
@@ -200,6 +200,10 @@ def __init_subclass__(cls, auto_wrap_output_keys=("transform",), **kwargs):
             if not hasattr(cls, method) or key not in auto_wrap_output_keys:
                 continue
             cls._sklearn_auto_wrap_output_keys.add(key)
+
+            # Only wrap methods defined by cls itself
+            if method not in cls.__dict__:
+                continue
             wrapped_method = _wrap_method_output(getattr(cls, method), key)
             setattr(cls, method, wrapped_method)
 
diff --git a/sklearn/utils/tests/test_set_output.py b/sklearn/utils/tests/test_set_output.py
@@ -237,3 +237,26 @@ def get_columns():
     X_np = np.asarray([[1, 3], [2, 4], [3, 5]])
     X_wrapped = _wrap_in_pandas_container(X_np, columns=get_columns)
     assert_array_equal(X_wrapped.columns, range(X_np.shape[1]))
+
+
+def test_set_output_mro():
+    """Check that multi-inheritance resolves to the correct class method.
+
+    Non-regression test gh-25293.
+    """
+
+    class Base(_SetOutputMixin):
+        def transform(self, X):
+            return "Base"  # noqa
+
+    class A(Base):
+        pass
+
+    class B(Base):
+        def transform(self, X):
+            return "B"
+
+    class C(A, B):
+        pass
+
+    assert C().transform(None) == "B"
