[MRG+1] Fix ug in BaseSearchCV.inverse_transform (scikit-learn#8348)

Author: Akshay0724

doc/whats_new.rst

@@ -153,6 +153,11 @@ Enhancements
 Bug fixes
 .........
 
+   - Fixed a bug where :func:`sklearn.model_selection.BaseSearchCV.inverse_transform`
+     returns self.best_estimator_.transform() instead of self.best_estimator_.inverse_transform()
+     :issue:`8344` by :user:`Akshay Gupta <Akshay0724>` 
+
+
    - Fixed a bug where :class:`sklearn.linear_model.RandomizedLasso` and
      :class:`sklearn.linear_model.RandomizedLogisticRegression` breaks for
      sparse input.

sklearn/model_selection/_search.py

@@ -530,7 +530,7 @@ def inverse_transform(self, Xt):
 
         """
         self._check_is_fitted('inverse_transform')
-        return self.best_estimator_.transform(Xt)
+        return self.best_estimator_.inverse_transform(Xt)
 
     @property
     def classes_(self):

sklearn/model_selection/tests/test_search.py

@@ -79,11 +79,15 @@ def fit(self, X, Y):
     def predict(self, T):
         return T.shape[0]
 
+    def transform(self, X):
+        return X + self.foo_param
+
+    def inverse_transform(self, X):
+        return X - self.foo_param
+
     predict_proba = predict
     predict_log_proba = predict
     decision_function = predict
-    transform = predict
-    inverse_transform = predict
 
     def score(self, X=None, Y=None):
         if self.foo_param > 1:
@@ -1305,3 +1309,12 @@ def _pop_time_keys(cv_results):
                                   per_param_scores[1])
         assert_array_almost_equal(per_param_scores[2],
                                   per_param_scores[3])
+
+
+def test_transform_inverse_transform_round_trip():
+    clf = MockClassifier()
+    grid_search = GridSearchCV(clf, {'foo_param': [1, 2, 3]}, verbose=3)
+
+    grid_search.fit(X, y)
+    X_round_trip = grid_search.inverse_transform(grid_search.transform(X))
+    assert_array_equal(X, X_round_trip)