BaseSearchCV._run_search raises NotImplementedError instead of being an abstractmethod (scikit-learn#12182)

adrinjalali · amueller · commit 239482ffdf14 · 2018-09-28T13:49:58.000-04:00
* _run_search raises NotImplementedError instead of being and abstractmethod

* add error message

* test for a BaseSearchCV child w/o a _run_search

* make the test python2 compatible, still in 0.20 zone.

* specify cv in tests not to trigger the related FutureWarning

* PEP8
diff --git a/sklearn/model_selection/_search.py b/sklearn/model_selection/_search.py
@@ -580,11 +580,10 @@ def classes_(self):
         self._check_is_fitted("classes_")
         return self.best_estimator_.classes_
 
-    @abstractmethod
     def _run_search(self, evaluate_candidates):
         """Repeatedly calls `evaluate_candidates` to conduct a search.
 
-        This method, implemented in sub-classes, makes it is possible to
+        This method, implemented in sub-classes, makes it possible to
         customize the the scheduling of evaluations: GridSearchCV and
         RandomizedSearchCV schedule evaluations for their whole parameter
         search space at once but other more sequential approaches are also
@@ -613,6 +612,7 @@ def _run_search(self, evaluate_candidates):
                 if score[0] < score[1]:
                     evaluate_candidates([{'C': 0.1}])
         """
+        raise NotImplementedError("_run_search not implemented.")
 
     def fit(self, X, y=None, groups=None, **fit_params):
         """Run fit with all sets of parameters.
diff --git a/sklearn/model_selection/tests/test_search.py b/sklearn/model_selection/tests/test_search.py
@@ -182,7 +182,6 @@ def test_parameter_grid():
 
 @pytest.mark.filterwarnings('ignore: The default of the `iid`')  # 0.22
 @pytest.mark.filterwarnings('ignore: You should specify a value')  # 0.22
-
 def test_grid_search():
     # Test that the best estimator contains the right value for foo_param
     clf = MockClassifier()
@@ -1678,6 +1677,27 @@ def _run_search(self, evaluate):
                    "Attribute %s not equal" % attr
 
 
+def test__custom_fit_no_run_search():
+    class NoRunSearchSearchCV(BaseSearchCV):
+        def __init__(self, estimator, **kwargs):
+            super(NoRunSearchSearchCV, self).__init__(estimator, **kwargs)
+
+        def fit(self, X, y=None, groups=None, **fit_params):
+            return self
+
+    # this should not raise any exceptions
+    NoRunSearchSearchCV(SVC(), cv=5).fit(X, y)
+
+    class BadSearchCV(BaseSearchCV):
+        def __init__(self, estimator, **kwargs):
+            super(BadSearchCV, self).__init__(estimator, **kwargs)
+
+    with pytest.raises(NotImplementedError,
+                       match="_run_search not implemented."):
+        # this should raise a NotImplementedError
+        BadSearchCV(SVC(), cv=5).fit(X, y)
+
+
 def test_deprecated_grid_search_iid():
     depr_message = ("The default of the `iid` parameter will change from True "
                     "to False in version 0.22")
