scikit-learn · rth · Jan 31, 2020 · Jan 29, 2020 · Jan 29, 2020 · Jan 29, 2020
diff --git a/sklearn/ensemble/_hist_gradient_boosting/gradient_boosting.py b/sklearn/ensemble/_hist_gradient_boosting/gradient_boosting.py
@@ -923,6 +923,8 @@ class HistGradientBoostingClassifier(BaseHistGradientBoosting,
 
     Attributes
     ----------
+    classes_ : array, shape = (n_classes,)
+        Class labels.
     n_iter_ : int
         The number of estimators as selected by early stopping (if
         n_iter_no_change is not None). Otherwise it corresponds to max_iter.

diff --git a/sklearn/ensemble/_stacking.py b/sklearn/ensemble/_stacking.py
@@ -312,6 +312,9 @@ class StackingClassifier(ClassifierMixin, _BaseStacking):
 
     Attributes
     ----------
+    classes_ : array, shape = (n_classes,)
+        Class labels.
+
     estimators_ : list of estimators
         The elements of the estimators parameter, having been fitted on the
         training data. If an estimator has been set to `'drop'`, it

diff --git a/sklearn/multioutput.py b/sklearn/multioutput.py
@@ -288,6 +288,9 @@ class MultiOutputClassifier(ClassifierMixin, _MultiOutputEstimator):
 
     Attributes
     ----------
+    classes_ : array, shape = (n_classes,)
+        Class labels.
+
     estimators_ : list of ``n_output`` estimators
         Estimators used for predictions.
 

diff --git a/sklearn/tests/test_docstring_parameters.py b/sklearn/tests/test_docstring_parameters.py
@@ -15,6 +15,7 @@
 from sklearn.utils._testing import check_docstring_parameters
 from sklearn.utils._testing import _get_func_name
 from sklearn.utils._testing import ignore_warnings
+from sklearn.utils._testing import all_estimators
 from sklearn.utils.deprecation import _is_deprecated
 from sklearn.externals._pep562 import Pep562
 
@@ -160,3 +161,15 @@ def test_tabs():
         assert '\t' not in source, ('"%s" has tabs, please remove them ',
                                     'or add it to theignore list'
                                     % modname)
+
+
+@pytest.mark.parametrize('name, Classifier',
+                         all_estimators(type_filter='classifier'))
+def test_classifier_docstring_attributes(name, Classifier):
+    docscrape = pytest.importorskip('numpydoc.docscrape')
+    from numpydoc import docscrape
+
+    doc = docscrape.ClassDoc(Classifier)
+    attributes = doc['Attributes']
+    assert attributes
+    assert 'classes_' in [att.name for att in attributes]
diff --git a/sklearn/utils/_mocking.py b/sklearn/utils/_mocking.py
@@ -61,6 +61,11 @@ class CheckingClassifier(ClassifierMixin, BaseEstimator):
     check_X
     foo_param
     expected_fit_params
+
+    Attributes
+    ----------
+    classes_
+
     """
     def __init__(self, check_y=None, check_X=None, foo_param=0,
                  expected_fit_params=None):