Make FrozenEstimator explicitly accept and ignore sample_weight (scikit-learn#30874)

Author: ogrisel

doc/whats_new/upcoming_changes/sklearn.frozen/30874.enhancement.rst

@@ -0,0 +1,3 @@
+- :class:`~frozen.FrozenEstimator` now explicitly accepts a `sample_weight`
+  argument in `fit` (and ignores it explicitly) to make it inspectable by
+  meta-estimators and testing frameworks. By :user:`Olivier Grisel <ogrisel>`

sklearn/frozen/_frozen.py

@@ -86,7 +86,7 @@ def __sklearn_is_fitted__(self):
         except NotFittedError:
             return False
 
-    def fit(self, X, y, *args, **kwargs):
+    def fit(self, X, y, sample_weight=None, *args, **kwargs):
         """No-op.
 
         As a frozen estimator, calling `fit` has no effect.
@@ -99,6 +99,9 @@ def fit(self, X, y, *args, **kwargs):
         y : object
             Ignored.
 
+        sample_weight : object
+            Ignored.
+
         *args : tuple
             Additional positional arguments. Ignored, but present for API compatibility
             with `self.estimator`.

sklearn/frozen/tests/test_frozen.py

@@ -26,7 +26,7 @@
 from sklearn.pipeline import make_pipeline
 from sklearn.preprocessing import RobustScaler, StandardScaler
 from sklearn.utils._testing import set_random_state
-from sklearn.utils.validation import check_is_fitted
+from sklearn.utils.validation import check_is_fitted, has_fit_parameter
 
 
 @pytest.fixture
@@ -221,3 +221,16 @@ def test_frozen_params():
     other_est = LocalOutlierFactor()
     frozen.set_params(estimator=other_est)
     assert frozen.get_params() == {"estimator": other_est}
+
+
+def test_frozen_ignores_sample_weight(regression_dataset):
+    X, y = regression_dataset
+    estimator = LinearRegression().fit(X, y)
+    frozen = FrozenEstimator(estimator)
+
+    # Should not raise: sample_weight is just ignored as it is not used.
+    frozen.fit(X, y, sample_weight=np.ones(len(y)))
+
+    # FrozenEstimator should have sample_weight in its signature to make it
+    # explicit that sample_weight is accepted and ignored intentionally.
+    assert has_fit_parameter(frozen, "sample_weight")