FIX Avoid setting legend when labels are None in RocCurveDisplay kwargs (#29727)

ArturoAmorQ · web-flow · commit 08eebc62a18e · 2025-01-13T12:26:05.000+05:00
diff --git a/doc/whats_new/upcoming_changes/sklearn.metrics/29727.fix.rst b/doc/whats_new/upcoming_changes/sklearn.metrics/29727.fix.rst
@@ -0,0 +1,3 @@
+- :class:`metrics.RocCurveDisplay` will no longer set a legend when
+  `label` is `None` in both the `line_kwargs` and the `chance_level_kw`.
+  By :user:`Arturo Amor <ArturoAmorQ>`
diff --git a/sklearn/metrics/_plot/roc_curve.py b/sklearn/metrics/_plot/roc_curve.py
@@ -185,7 +185,10 @@ def plot(
         if despine:
             _despine(self.ax_)
 
-        if "label" in line_kwargs or "label" in chance_level_kw:
+        if (
+            line_kwargs.get("label") is not None
+            or chance_level_kw.get("label") is not None
+        ):
             self.ax_.legend(loc="lower right")
 
         return self
diff --git a/sklearn/metrics/_plot/tests/test_roc_curve_display.py b/sklearn/metrics/_plot/tests/test_roc_curve_display.py
@@ -127,12 +127,14 @@ def test_roc_curve_display_plotting(
 
 
 @pytest.mark.parametrize("plot_chance_level", [True, False])
+@pytest.mark.parametrize("label", [None, "Test Label"])
 @pytest.mark.parametrize(
     "chance_level_kw",
     [
         None,
         {"linewidth": 1, "color": "red", "linestyle": "-", "label": "DummyEstimator"},
         {"lw": 1, "c": "red", "ls": "-", "label": "DummyEstimator"},
+        {"lw": 1, "color": "blue", "ls": "-", "label": None},
     ],
 )
 @pytest.mark.parametrize(
@@ -144,6 +146,7 @@ def test_roc_curve_chance_level_line(
     data_binary,
     plot_chance_level,
     chance_level_kw,
+    label,
     constructor_name,
 ):
     """Check the chance level line plotting behaviour."""
@@ -160,6 +163,7 @@ def test_roc_curve_chance_level_line(
             lr,
             X,
             y,
+            label=label,
             alpha=0.8,
             plot_chance_level=plot_chance_level,
             chance_level_kw=chance_level_kw,
@@ -168,6 +172,7 @@ def test_roc_curve_chance_level_line(
         display = RocCurveDisplay.from_predictions(
             y,
             y_pred,
+            label=label,
             alpha=0.8,
             plot_chance_level=plot_chance_level,
             chance_level_kw=chance_level_kw,
@@ -193,7 +198,6 @@ def test_roc_curve_chance_level_line(
         assert display.chance_level_.get_linestyle() == "--"
         assert display.chance_level_.get_label() == "Chance level (AUC = 0.5)"
     elif plot_chance_level:
-        assert display.chance_level_.get_label() == chance_level_kw["label"]
         if "c" in chance_level_kw:
             assert display.chance_level_.get_color() == chance_level_kw["c"]
         else:
@@ -206,6 +210,17 @@ def test_roc_curve_chance_level_line(
             assert display.chance_level_.get_linestyle() == chance_level_kw["ls"]
         else:
             assert display.chance_level_.get_linestyle() == chance_level_kw["linestyle"]
+        # Checking for legend behaviour
+        if label is not None or chance_level_kw.get("label") is not None:
+            legend = display.ax_.get_legend()
+            assert legend is not None  #  Legend should be present if any label is set
+            legend_labels = [text.get_text() for text in legend.get_texts()]
+            if label is not None:
+                assert label in legend_labels
+            if chance_level_kw.get("label") is not None:
+                assert chance_level_kw["label"] in legend_labels
+        else:
+            assert display.ax_.get_legend() is None
 
 
 @pytest.mark.parametrize(

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+- :class:`metrics.RocCurveDisplay` will no longer set a legend when
	`2`	+ `label` is `None` in both the `line_kwargs` and the `chance_level_kw`.
	`3`	+ By :user:`Arturo Amor <ArturoAmorQ>`