scikit-learn · adrinjalali · Jun 12, 2025 · Jun 14, 2025 · Jun 14, 2025 · Jun 14, 2025
diff --git a/doc/whats_new/upcoming_changes/metadata-routing/32111.fix.rst b/doc/whats_new/upcoming_changes/metadata-routing/32111.fix.rst
@@ -0,0 +1,3 @@
+- If a class explicitly defines a `set_{method}_request` method, it will not be
+  overridden by the metadata routing machinery.
+  By `Adrin Jalali`_
diff --git a/sklearn/tests/test_metadata_routing.py b/sklearn/tests/test_metadata_routing.py
@@ -1162,3 +1162,42 @@ def fit(self, X, y, sample_weight=None):
     # Test positional arguments error after making the descriptor method unbound.
     with pytest.raises(TypeError, match=error_message):
         A().set_fit_request(True)
+
+
+@config_context(enable_metadata_routing=True)
+def test_removing_metadata_in_subclass_correctly_works():
+    """Test that removing a metadata with UNUSED marker affects child's method."""
+
+    class A(ConsumingClassifier):
+        __metadata_request__score = {
+            "sample_weight": metadata_routing.UNUSED,
+            "metadata": metadata_routing.UNUSED,
+        }
+
+    # Here we make sure that the parent class has the method as usual
+    assert hasattr(ConsumingClassifier(), "set_score_request")
+    # And that the child class doesn't have it since all metadata for the score method
+    # are removed.
+    with pytest.raises(
+        TypeError,
+        match=re.escape(
+            "Unexpected args: {'sample_weight'} in score. Accepted arguments are: set()"
+        ),
+    ):
+        A().set_score_request(sample_weight=True)
+
+
+@config_context(enable_metadata_routing=True)
+def test_explicitly_defined_set_method_request_is_not_overriden():
+    """Test that explicitly defined set_{method}_request is not overridden."""
+
+    class A(BaseEstimator):
+        def set_score_request(self, sample_weight=None, metadata=None):
+            return self  # pragma: no cover
+
+    class B(A):
+        def score(self, X, y=None):
+            pass  # pragma: no cover
+
+    # This should work as usual since the method is explicitly defined.
+    B().set_score_request(sample_weight=True)
diff --git a/sklearn/utils/_metadata_requests.py b/sklearn/utils/_metadata_requests.py
@@ -1438,14 +1438,35 @@ def __init_subclass__(cls, **kwargs):
         ----------
         .. [1] https://www.python.org/dev/peps/pep-0487
         """
+
+        def is_RequestMethod(obj, name: str):
+            value = inspect.getattr_static(obj, name)
+            return isinstance(value, RequestMethod)
+
         try:
             for method in SIMPLE_METHODS:
+                set_method_name = f"set_{method}_request"
                 requests = cls._get_class_level_metadata_request_values(method)
-                if not requests:
+                if hasattr(cls, set_method_name) and not is_RequestMethod(
+                    cls, set_method_name
+                ):
+                    # The method is not a descriptor, which means it's explicitly\
+                    # defined in the class, therefore we skip overriding it with a
+                    # descriptor here.
+                    # This happens, for instance in Scorers where the
+                    # `set_score_request` method is defined in the class.
+                    continue
+
+                if not requests and not hasattr(cls, set_method_name):
+                    # It can be the case that requests here is empty due to removing
+                    # metadata with an UNUSED marker, and that the parent class has
+                    # the method already. In this case, we cannot remove the method
+                    # since it exists in the parent class, and instead we set it with
+                    # an empty set of requests.
                     continue
                 setattr(
                     cls,
-                    f"set_{method}_request",
+                    set_method_name,
                     RequestMethod(method, sorted(requests)),
                 )
         except Exception: