scikit-learn · adrinjalali · May 4, 2023 · Mar 31, 2023 · Apr 1, 2023 · Apr 1, 2023
diff --git a/sklearn/metrics/_scorer.py b/sklearn/metrics/_scorer.py
@@ -18,8 +18,9 @@
 #          Arnaud Joly <arnaud.v.joly@gmail.com>
 # License: Simplified BSD
 
-from functools import partial
 from collections import Counter
+from inspect import signature
+from functools import partial
 from traceback import format_exc
 
 import numpy as np
@@ -64,20 +65,23 @@
 
 from ..utils.multiclass import type_of_target
 from ..base import is_regressor
+from ..utils._response import _get_response_values
 from ..utils._param_validation import HasMethods, StrOptions, validate_params
 
 
-def _cached_call(cache, estimator, method, *args, **kwargs):
+def _cached_call(cache, estimator, response_method, *args, **kwargs):
     """Call estimator with method and args and kwargs."""
-    if cache is None:
-        return getattr(estimator, method)(*args, **kwargs)
+    if cache is not None and response_method in cache:
+        return cache[response_method]
+
+    result, _ = _get_response_values(
+        estimator, *args, response_method=response_method, **kwargs
+    )
+
+    if cache is not None:
+        cache[response_method] = result
 
-    try:
-        return cache[method]
-    except KeyError:
-        result = getattr(estimator, method)(*args, **kwargs)
-        cache[method] = result
-        return result
+    return result
 
 
 class _MultimetricScorer:
@@ -162,40 +166,13 @@ def __init__(self, score_func, sign, kwargs):
         self._score_func = score_func
         self._sign = sign
 
-    @staticmethod
-    def _check_pos_label(pos_label, classes):
-        if pos_label not in list(classes):
-            raise ValueError(f"pos_label={pos_label} is not a valid label: {classes}")
-
-    def _select_proba_binary(self, y_pred, classes):
-        """Select the column of the positive label in `y_pred` when
-        probabilities are provided.
-
-        Parameters
-        ----------
-        y_pred : ndarray of shape (n_samples, n_classes)
-            The prediction given by `predict_proba`.
-
-        classes : ndarray of shape (n_classes,)
-            The class labels for the estimator.
-
-        Returns
-        -------
-        y_pred : ndarray of shape (n_samples,)
-            Probability predictions of the positive class.
-        """
-        if y_pred.shape[1] == 2:
-            pos_label = self._kwargs.get("pos_label", classes[1])
-            self._check_pos_label(pos_label, classes)
-            col_idx = np.flatnonzero(classes == pos_label)[0]
-            return y_pred[:, col_idx]
-
-        err_msg = (
-            f"Got predict_proba of shape {y_pred.shape}, but need "
-            f"classifier with two classes for {self._score_func.__name__} "
-            "scoring"
-        )
-        raise ValueError(err_msg)
+    def _get_pos_label(self):
+        if "pos_label" in self._kwargs:
+            return self._kwargs["pos_label"]
+        score_func_params = signature(self._score_func).parameters
+        if "pos_label" in score_func_params:
+            return score_func_params["pos_label"].default
+        return None
 
     def __repr__(self):
         kwargs_string = "".join(
@@ -311,14 +288,7 @@ def _score(self, method_caller, clf, X, y, sample_weight=None):
         score : float
             Score function applied to prediction of estimator on X.
         """
-
-        y_type = type_of_target(y)
-        y_pred = method_caller(clf, "predict_proba", X)
-        if y_type == "binary" and y_pred.shape[1] <= 2:
-            # `y_type` could be equal to "binary" even in a multi-class
-            # problem: (when only 2 class are given to `y_true` during scoring)
-            # Thus, we need to check for the shape of `y_pred`.
-            y_pred = self._select_proba_binary(y_pred, clf.classes_)
+        y_pred = method_caller(clf, "predict_proba", X, pos_label=self._get_pos_label())
         if sample_weight is not None:
             return self._sign * self._score_func(
                 y, y_pred, sample_weight=sample_weight, **self._kwargs
@@ -369,26 +339,17 @@ def _score(self, method_caller, clf, X, y, sample_weight=None):
         if is_regressor(clf):
             y_pred = method_caller(clf, "predict", X)
         else:
+            pos_label = self._get_pos_label()
             try:
-                y_pred = method_caller(clf, "decision_function", X)
+                y_pred = method_caller(clf, "decision_function", X, pos_label=pos_label)
 
                 if isinstance(y_pred, list):
                     # For multi-output multi-class estimator
                     y_pred = np.vstack([p for p in y_pred]).T
-                elif y_type == "binary" and "pos_label" in self._kwargs:
-                    self._check_pos_label(self._kwargs["pos_label"], clf.classes_)
-                    if self._kwargs["pos_label"] == clf.classes_[0]:
-                        # The implicit positive class of the binary classifier
-                        # does not match `pos_label`: we need to invert the
-                        # predictions
-                        y_pred *= -1
 
             except (NotImplementedError, AttributeError):
-                y_pred = method_caller(clf, "predict_proba", X)
-
-                if y_type == "binary":
-                    y_pred = self._select_proba_binary(y_pred, clf.classes_)
-                elif isinstance(y_pred, list):
+                y_pred = method_caller(clf, "predict_proba", X, pos_label=pos_label)
+                if isinstance(y_pred, list):
                     y_pred = np.vstack([p[:, -1] for p in y_pred]).T
 
         if sample_weight is not None:

diff --git a/sklearn/metrics/tests/test_score_objects.py b/sklearn/metrics/tests/test_score_objects.py
@@ -759,13 +759,18 @@ def test_multimetric_scorer_calls_method_once(
     X, y = np.array([[1], [1], [0], [0], [0]]), np.array([0, 1, 1, 1, 0])
 
     mock_est = Mock()
-    fit_func = Mock(return_value=mock_est)
-    predict_func = Mock(return_value=y)
+    mock_est._estimator_type = "classifier"
+    fit_func = Mock(return_value=mock_est, name="fit")
+    fit_func.__name__ = "fit"
+    predict_func = Mock(return_value=y, name="predict")
+    predict_func.__name__ = "predict"
 
     pos_proba = np.random.rand(X.shape[0])
     proba = np.c_[1 - pos_proba, pos_proba]
-    predict_proba_func = Mock(return_value=proba)
-    decision_function_func = Mock(return_value=pos_proba)
+    predict_proba_func = Mock(return_value=proba, name="predict_proba")
+    predict_proba_func.__name__ = "predict_proba"
+    decision_function_func = Mock(return_value=pos_proba, name="decision_function")
+    decision_function_func.__name__ = "decision_function"
 
     mock_est.fit = fit_func
     mock_est.predict = predict_func
@@ -961,7 +966,7 @@ def test_multiclass_roc_no_proba_scorer_errors(scorer_name):
         n_classes=3, n_informative=3, n_samples=20, random_state=0
     )
     lr = Perceptron().fit(X, y)
-    msg = "'Perceptron' object has no attribute 'predict_proba'"
+    msg = "Perceptron has none of the following attributes: predict_proba."
     with pytest.raises(AttributeError, match=msg):
         scorer(lr, X, y)
 

diff --git a/sklearn/utils/_response.py b/sklearn/utils/_response.py
@@ -19,9 +19,6 @@ def _get_response_values(
     The response values are predictions, one scalar value for each sample in X
     that depends on the specific choice of `response_method`.
 
-    This helper only accepts multiclass classifiers with the `predict` response
-    method.
-
     If `estimator` is a binary classifier, also return the label for the
     effective positive class.
 
@@ -75,15 +72,8 @@ def _get_response_values(
     if is_classifier(estimator):
         prediction_method = _check_response_method(estimator, response_method)
         classes = estimator.classes_
-
         target_type = "binary" if len(classes) <= 2 else "multiclass"
 
-        if target_type == "multiclass" and prediction_method.__name__ != "predict":
-            raise ValueError(
-                "With a multiclass estimator, the response method should be "
-                f"predict, got {prediction_method.__name__} instead."
-            )
-
         if pos_label is not None and pos_label not in classes.tolist():
             raise ValueError(
                 f"pos_label={pos_label} is not a valid label: It should be "

diff --git a/sklearn/utils/tests/test_response.py b/sklearn/utils/tests/test_response.py
@@ -6,7 +6,7 @@
     LinearRegression,
     LogisticRegression,
 )
-from sklearn.svm import SVC
+from sklearn.preprocessing import scale
 from sklearn.tree import DecisionTreeClassifier, DecisionTreeRegressor
 from sklearn.utils._mocking import _MockEstimatorOnOffPrediction
 from sklearn.utils._testing import assert_allclose, assert_array_equal
@@ -15,6 +15,8 @@
 
 
 X, y = load_iris(return_X_y=True)
+# scale the data to avoid ConvergenceWarning with LogisticRegression
+X = scale(X, copy=False)
 X_binary, y_binary = X[:100], y[:100]
 
 
@@ -29,25 +31,6 @@ def test_get_response_values_regressor_error(response_method):
         _get_response_values(my_estimator, X, response_method=response_method)
 
 
-@pytest.mark.parametrize(
-    "estimator, response_method",
-    [
-        (DecisionTreeClassifier(), "predict_proba"),
-        (SVC(), "decision_function"),
-    ],
-)
-def test_get_response_values_error_multiclass_classifier(estimator, response_method):
-    """Check that we raise an error with multiclass classifier and requesting
-    response values different from `predict`."""
-    X, y = make_classification(
-        n_samples=10, n_clusters_per_class=1, n_classes=3, random_state=0
-    )
-    classifier = estimator.fit(X, y)
-    err_msg = "With a multiclass estimator, the response method should be predict"
-    with pytest.raises(ValueError, match=err_msg):
-        _get_response_values(classifier, X, response_method=response_method)
-
-
 def test_get_response_values_regressor():
     """Check the behaviour of `_get_response_values` with regressor."""
     X, y = make_regression(n_samples=10, random_state=0)
@@ -227,3 +210,25 @@ def test_get_response_decision_function():
     )
     np.testing.assert_allclose(y_score, classifier.decision_function(X_binary) * -1)
     assert pos_label == 0
+
+
+@pytest.mark.parametrize(
+    "estimator, response_method",
+    [
+        (DecisionTreeClassifier(max_depth=2, random_state=0), "predict_proba"),
+        (LogisticRegression(), "decision_function"),
+    ],
+)
+def test_get_response_values_multiclass(estimator, response_method):
+    """Check that we can call `_get_response_values` with a multiclass estimator.
+    It should return the predictions untouched.
+    """
+    estimator.fit(X, y)
+    predictions, pos_label = _get_response_values(
+        estimator, X, response_method=response_method
+    )
+
+    assert pos_label is None
+    assert predictions.shape == (X.shape[0], len(estimator.classes_))
+    if response_method == "predict_proba":
+        assert np.logical_and(predictions >= 0, predictions <= 1).all()