Fix IndexError for pyplot.legend() when plotting empty bar chart with label (#13551)

choyiny · jklymak · commit a06ed93fdba3 · 2019-03-02T12:47:26.000-08:00
* FIX: legend crashes when bar chart is empty with label

* add test with generating legend with empty bar chart

* remove image_comparison from legend test case
diff --git a/lib/matplotlib/legend_handler.py b/lib/matplotlib/legend_handler.py
@@ -35,7 +35,9 @@ def legend_artist(self, legend, orig_handle, fontsize, handlebox)
 
 
 def update_from_first_child(tgt, src):
-    tgt.update_from(src.get_children()[0])
+    first_child = next(iter(src.get_children()), None)
+    if first_child is not None:
+        tgt.update_from(first_child)
 
 
 class HandlerBase(object):
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -477,6 +477,14 @@ def test_handler_numpoints():
     ax.legend(numpoints=0.5)
 
 
+def test_empty_bar_chart_with_legend():
+    """Test legend when bar chart is empty with a label."""
+    # related to issue #13003. Calling plt.legend() should not
+    # raise an IndexError.
+    plt.bar([], [], label='test')
+    plt.legend()
+
+
 def test_shadow_framealpha():
     # Test if framealpha is activated when shadow is True
     # and framealpha is not explicitly passed'''
