Hide unlabeled traces from legend when figure has a legend

Author: robertoffmoura

plotly/matplotlylib/renderer.py

@@ -447,11 +447,15 @@ def draw_marked_line(self, **props):
             label = props["label"]
             # matplotlib uses "_nolegend_" and auto-generated "_childN"
             # labels for artists that must not appear in a legend
-            if isinstance(label, str) and label.startswith("_"):
+            if not label or (isinstance(label, str) and label.startswith("_")):
                 label = None
+                showlegend = False
+            else:
+                showlegend = None
             marked_line = go.Scatter(
                 mode=mode,
                 name=label,
+                showlegend=showlegend,
                 x=[xy_pair[0] for xy_pair in props["data"]],
                 y=[xy_pair[1] for xy_pair in props["data"]],
                 xaxis="x{0}".format(self.axis_ct),

plotly/matplotlylib/tests/test_renderer.py

@@ -323,6 +323,23 @@ def test_no_legend_entries_for_internal_mpl_labels():
     assert all(t.name is None for t in plotly_fig.data)
 
 
+def test_unlabeled_traces_hidden_from_legend_when_figure_has_legend():
+    """Traces without labels must have showlegend=False when a figure has a legend."""
+    fig, ax = plt.subplots()
+    ax.plot([0, 1], [0, 1], label="Labeled line")
+    ax.plot([0, 1], [1, 0])  # Unlabeled line
+    ax.legend()
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert plotly_fig.layout.showlegend == True
+    assert len(plotly_fig.data) == 2
+    assert plotly_fig.data[0].name == "Labeled line"
+    assert plotly_fig.data[0].showlegend is not False
+    assert plotly_fig.data[1].name is None
+    assert plotly_fig.data[1].showlegend is False
+
+
 def test_custom_date_xtickvals_are_converted():
     """Custom tick values on a date axis must be converted to date strings,
     not left as raw matplotlib date numbers or datetime objects."""