Merge pull request matplotlib#27711 from saranti/boxlegend

Fix boxplot legend entries part 2

Author: dstansby

lib/matplotlib/axes/_axes.py

@@ -4004,6 +4004,9 @@ def boxplot(self, x, notch=None, sym=None, vert=None, whis=None,
             if 'color' in boxprops:
                 boxprops['edgecolor'] = boxprops.pop('color')
 
+        if labels:
+            boxprops['label'] = labels
+
         # if non-default sym value, put it into the flier dictionary
         # the logic for providing the default symbol ('b+') now lives
         # in bxp in the initial value of flierkw
@@ -4316,13 +4319,16 @@ def do_patch(xs, ys, **kwargs):
                 do_box = do_patch if patch_artist else do_plot
                 boxes.append(do_box(box_x, box_y, **box_kw))
             # draw the whiskers
+            whisker_kw.setdefault('label', '_nolegend_')
             whiskers.append(do_plot(whis_x, whislo_y, **whisker_kw))
             whiskers.append(do_plot(whis_x, whishi_y, **whisker_kw))
             # maybe draw the caps
             if showcaps:
+                cap_kw.setdefault('label', '_nolegend_')
                 caps.append(do_plot(cap_x, cap_lo, **cap_kw))
                 caps.append(do_plot(cap_x, cap_hi, **cap_kw))
             # draw the medians
+            median_kw.setdefault('label', '_nolegend_')
             medians.append(do_plot(med_x, med_y, **median_kw))
             # maybe draw the means
             if showmeans:
@@ -4335,6 +4341,7 @@ def do_patch(xs, ys, **kwargs):
                     means.append(do_plot([pos], [stats['mean']], **mean_kw))
             # maybe draw the fliers
             if showfliers:
+                flier_kw.setdefault('label', '_nolegend_')
                 flier_x = np.full(len(stats['fliers']), pos, dtype=np.float64)
                 flier_y = stats['fliers']
                 fliers.append(do_plot(flier_x, flier_y, **flier_kw))

lib/matplotlib/tests/test_legend.py

@@ -1427,3 +1427,33 @@ def test_legend_text():
         leg_bboxes.append(
             leg.get_window_extent().transformed(ax.transAxes.inverted()))
     assert_allclose(leg_bboxes[1].bounds, leg_bboxes[0].bounds)
+
+
+def test_boxplot_legend():
+    # Test that boxplot legends handles are patches
+    # and labels are generated from boxplot's labels parameter.
+    fig, axs = plt.subplots()
+    A = 5*np.random.rand(100, 1)
+    B = 10*np.random.rand(100, 1) - 5
+    C = 7*np.random.rand(100, 1) - 5
+    labels = ['a', 'b', 'c']
+
+    bp0 = axs.boxplot(A, positions=[0], patch_artist=True, labels=labels[0])
+    bp1 = axs.boxplot(B, positions=[1], patch_artist=True, labels=labels[1])
+    bp2 = axs.boxplot(C, positions=[2], patch_artist=True, labels=labels[2])
+    # red, blue, green
+    colors = [(1.0, 0.0, 0.0, 1), (0.0, 0.0, 1.0, 1), (0.0, 0.5, 0.0, 1)]
+    box_list = [bp0, bp1, bp2]
+    # Set colors to the boxes
+    lbl_index = 0
+    for b_plot, color in zip(box_list, colors):
+        for patch in b_plot['boxes']:
+            patch.set_color(color)
+            lbl_index += 1
+
+    legend = axs.legend()
+    for index, handle in enumerate(legend.legend_handles):
+        assert isinstance(handle, mpl.patches.Rectangle)
+        assert handle.get_facecolor() == colors[index]
+        assert handle.get_edgecolor() == colors[index]
+        assert handle.get_label() == labels[index]