Broken estimator_ attribute on some ensemble models #25588
Description
Describe the bug
Several ensemble models raise an error when trying to access the existing estimator_ attribute.
The problem is that this property tries to access self._estimator, which is set by sklearn.ensemble.BaseEnsemble._validate_estimator, but that method is not called by all subclasses.
scikit-learn/sklearn/ensemble/_base.py
Line 151 in 4c8813e
For VotingClassifier and VotingRegressor, it's understandable IMO, but the error message could be better. For gradient boosting, estimator_ could return something useful.
More as a reminder to myself, _validate_estimator is being rewritten in #24250 to return the estimator instead of setting it inplace.
Steps/Code to Reproduce
import sklearn.ensemble
from sklearn.neighbors import KNeighborsClassifier, KNeighborsRegressor
estimators = [
sklearn.ensemble.AdaBoostClassifier(),
sklearn.ensemble.AdaBoostRegressor(),
sklearn.ensemble.BaggingClassifier(),
sklearn.ensemble.BaggingRegressor(),
sklearn.ensemble.ExtraTreesClassifier(),
sklearn.ensemble.ExtraTreesRegressor(),
sklearn.ensemble.GradientBoostingClassifier(),
sklearn.ensemble.GradientBoostingRegressor(),
sklearn.ensemble.HistGradientBoostingClassifier(),
sklearn.ensemble.HistGradientBoostingRegressor(),
sklearn.ensemble.RandomForestClassifier(),
sklearn.ensemble.RandomForestRegressor(),
sklearn.ensemble.VotingClassifier([('5', KNeighborsClassifier(5)), ('10', KNeighborsClassifier(10))]),
sklearn.ensemble.VotingRegressor([('5', KNeighborsRegressor(5)), ('10', KNeighborsRegressor(10))]),
]
X, y = [[1], [2]], [0, 1]
msg = "Got {} error when trying to access .estimator_ in {}"
for estimator in estimators:
estimator.fit(X, y)
try:
estimator.estimator_
except Exception as e:
print(msg.format(e.__class__.__name__, estimator.__class__.__name__))Expected Results
No error is printed.
Actual Results
Got AttributeError error when trying to access .estimator_ in GradientBoostingClassifier
Got AttributeError error when trying to access .estimator_ in GradientBoostingRegressor
Got AttributeError error when trying to access .estimator_ in HistGradientBoostingClassifier
Got AttributeError error when trying to access .estimator_ in HistGradientBoostingRegressor
Got AttributeError error when trying to access .estimator_ in VotingClassifier
Got AttributeError error when trying to access .estimator_ in VotingRegressor
Versions
System:
python: 3.10.9 | packaged by conda-forge | (main, Feb 2 2023, 20:20:04) [GCC 11.3.0]
executable: /home/name/anaconda3/envs/skops/bin/python
machine: Linux-5.15.0-60-generic-x86_64-with-glibc2.35
Python dependencies:
sklearn: 1.2.0
pip: 22.3.1
setuptools: 65.5.1
numpy: 1.23.5
scipy: 1.9.3
Cython: None
pandas: 1.5.3
matplotlib: 3.6.3
joblib: 1.2.0
threadpoolctl: 3.1.0
Built with OpenMP: True
threadpoolctl info:
user_api: blas
internal_api: openblas
prefix: libopenblas
filepath: /home/name/anaconda3/envs/skops/lib/libopenblasp-r0.3.21.so
version: 0.3.21
threading_layer: pthreads
architecture: Haswell
num_threads: 8
user_api: openmp
internal_api: openmp
prefix: libgomp
filepath: /home/name/anaconda3/envs/skops/lib/libgomp.so.1.0.0
version: None
num_threads: 8