BUG: Fixes _BaseCompostion._set_params broken where there are no estimators (scikit-learn#11333)

Author: thomasjpfan

sklearn/compose/tests/test_column_transformer.py

@@ -794,6 +794,11 @@ def test_column_transformer_no_estimators():
  assert ct.transformers_[-1][2] == [0, 1, 2]
 
 
+def test_column_transformer_no_estimators_set_params():
+ ct = ColumnTransformer([]).set_params(n_jobs=2)
+ assert ct.n_jobs == 2
+
+
 def test_column_transformer_callable_specifier():
  # assert that function gets the full array / dataframe
  X_array = np.array([[0, 1, 2], [2, 4, 6]]).T

sklearn/utils/metaestimators.py

@@ -41,7 +41,10 @@ def _set_params(self, attr, **params):
  if attr in params:
  setattr(self, attr, params.pop(attr))
  # 2. Step replacement
- names, _ = zip(*getattr(self, attr))
+ items = getattr(self, attr)
+ names = []
+ if items:
+ names, _ = zip(*items)
  for name in list(six.iterkeys(params)):
  if '__' not in name and name in names:
  self._replace_estimator(attr, name, params.pop(name))