scikit-learn · thomasjpfan · Feb 8, 2023 · Jan 12, 2023 · Jan 13, 2023 · Jan 13, 2023
diff --git a/doc/whats_new/v1.3.rst b/doc/whats_new/v1.3.rst
@@ -206,6 +206,14 @@ Changelog
   The `sample_interval_` attribute is deprecated and will be removed in 1.5.
   :pr:`25190` by :user:`Vincent Maladière <Vincent-Maladiere>`.
 
+:mod:`sklearn.tree`
+...................
+
+- |Enhancement| Adds a `class_names` parameter to
+  :func:`tree.export_text`. This allows specifying the parameter `class_names`
+  for each target class in ascending numerical order.
+  :pr:`25387` by :user:`William M <Akbeeh>` and :user:`crispinlogan <crispinlogan>`.
+
 :mod:`sklearn.utils`
 ....................
 

diff --git a/sklearn/tree/_export.py b/sklearn/tree/_export.py
@@ -923,6 +923,7 @@ def export_text(
     decision_tree,
     *,
     feature_names=None,
+    class_names=None,
     max_depth=10,
     spacing=3,
     decimals=2,
@@ -943,6 +944,17 @@ def export_text(
         A list of length n_features containing the feature names.
         If None generic names will be used ("feature_0", "feature_1", ...).
 
+    class_names : list or None, default=None
+        Names of each of the target classes in ascending numerical order.
+        Only relevant for classification and not supported for multi-output.
+
+        - if `None`, the class names are delegated to `decision_tree.classes_`;
+        - if a list, then `class_names` will be used as class names instead
+          of `decision_tree.classes_`. The length of `class_names` must match
+          the length of `decision_tree.classes_`.
+
+        .. versionadded:: 1.3
+
     max_depth : int, default=10
         Only the first max_depth levels of the tree are exported.
         Truncated branches will be marked with "...".
@@ -986,7 +998,15 @@ def export_text(
     check_is_fitted(decision_tree)
     tree_ = decision_tree.tree_
     if is_classifier(decision_tree):
-        class_names = decision_tree.classes_
+        if class_names is None:
+            class_names = decision_tree.classes_
+        elif len(class_names) != len(decision_tree.classes_):
+            raise ValueError(
+                "When `class_names` is a list, it should contain as"
+                " many items as `decision_tree.classes_`. Got"
+                f" {len(class_names)} while the tree was fitted with"
+                f" {len(decision_tree.classes_)} classes."
+            )
     right_child_fmt = "{} {} <= {}\n"
     left_child_fmt = "{} {} >  {}\n"
     truncation_fmt = "{} {}\n"

diff --git a/sklearn/tree/tests/test_export.py b/sklearn/tree/tests/test_export.py
@@ -357,6 +357,13 @@ def test_export_text_errors():
     err_msg = "feature_names must contain 2 elements, got 1"
     with pytest.raises(ValueError, match=err_msg):
         export_text(clf, feature_names=["a"])
+    err_msg = (
+        "When `class_names` is a list, it should contain as"
+        " many items as `decision_tree.classes_`. Got 1 while"
+        " the tree was fitted with 2 classes."
+    )
+    with pytest.raises(ValueError, match=err_msg):
+        export_text(clf, class_names=["a"])
     err_msg = "decimals must be >= 0, given -1"
     with pytest.raises(ValueError, match=err_msg):
         export_text(clf, decimals=-1)
@@ -394,6 +401,16 @@ def test_export_text():
     ).lstrip()
     assert export_text(clf, feature_names=["a", "b"]) == expected_report
 
+    expected_report = dedent(
+        """
+    |--- feature_1 <= 0.00
+    |   |--- class: cat
+    |--- feature_1 >  0.00
+    |   |--- class: dog
+    """
+    ).lstrip()
+    assert export_text(clf, class_names=["cat", "dog"]) == expected_report
+
     expected_report = dedent(
         """
     |--- feature_1 <= 0.00