API add named_transformers attribute to FeatureUnion (scikit-learn#20331)

crflynn · glemaitre · ogrisel · glemaitre · commit f77b3c6dbffe · 2022-10-31T11:25:38.000+01:00
Co-authored-by: Guillaume Lemaitre &lt;g.lemaitre58@gmail.com&gt;
Co-authored-by: Olivier Grisel &lt;olivier.grisel@ensta.org&gt;
diff --git a/doc/whats_new/v1.2.rst b/doc/whats_new/v1.2.rst
@@ -528,6 +528,10 @@ Changelog
   be used when one of the transformers in the :class:`pipeline.FeatureUnion` is
   `"passthrough"`. :pr:`24058` by :user:`Diederik Perdok <diederikwp>`
 
+- |Enhancement| The :class:`FeatureUnion` class now has a `named_transformers`
+  attribute for accessing transformers by name.
+  :pr:`20331` by :user:`Christopher Flynn <crflynn>`.
+
 :mod:`sklearn.preprocessing`
 ............................
 
diff --git a/sklearn/pipeline.py b/sklearn/pipeline.py
@@ -959,6 +959,14 @@ class FeatureUnion(TransformerMixin, _BaseComposition):
 
     Attributes
     ----------
+    named_transformers : :class:`~sklearn.utils.Bunch`
+        Dictionary-like object, with the following attributes.
+        Read-only attribute to access any transformer parameter by user
+        given name. Keys are transformer names and values are
+        transformer parameters.
+
+        .. versionadded:: 1.2
+
     n_features_in_ : int
         Number of features seen during :term:`fit`. Only defined if the
         underlying first transformer in `transformer_list` exposes such an
@@ -1017,6 +1025,11 @@ def set_output(self, transform=None):
             _safe_set_output(step, transform=transform)
         return self
 
+    @property
+    def named_transformers(self):
+        # Use Bunch object to improve autocomplete
+        return Bunch(**dict(self.transformer_list))
+
     def get_params(self, deep=True):
         """Get parameters for this estimator.
 
diff --git a/sklearn/tests/test_pipeline.py b/sklearn/tests/test_pipeline.py
@@ -524,6 +524,19 @@ def test_feature_union():
     fs.fit(X, y)
 
 
+def test_feature_union_named_transformers():
+    """Check the behaviour of `named_transformers` attribute."""
+    transf = Transf()
+    noinvtransf = NoInvTransf()
+    fs = FeatureUnion([("transf", transf), ("noinvtransf", noinvtransf)])
+    assert fs.named_transformers["transf"] == transf
+    assert fs.named_transformers["noinvtransf"] == noinvtransf
+
+    # test named attribute
+    assert fs.named_transformers.transf == transf
+    assert fs.named_transformers.noinvtransf == noinvtransf
+
+
 def test_make_union():
     pca = PCA(svd_solver="full")
     mock = Transf()
