Merge pull request #24759 from Marvvxi/reverse_legend

story645 · timhoffm · web-flow · commit edfd3b4c1b96 · 2022-12-25T01:11:17.000-05:00
Legend: added *reverse* parameter that reverses order of labels and handles in legend and tests for *reverse* parameter

added what's new entry for legend(..., reverse=True), test for checking the displayed legend is reversed, and  .. versionadded tag to reverse parameter

Co-authored-by: Tim Hoffmann &lt;2836374+timhoffm@users.noreply.github.com&gt;
diff --git a/doc/users/next_whats_new/reverse_legend.rst b/doc/users/next_whats_new/reverse_legend.rst
@@ -0,0 +1,4 @@
+Reversed order of legend entries
+--------------------------------
+The order of legend entries can now be reversed by passing ``reverse=True`` to
+`~.Axes.legend`.
diff --git a/lib/matplotlib/legend.py b/lib/matplotlib/legend.py
@@ -209,6 +209,12 @@ def _update_bbox_to_anchor(self, loc_in_canvas):
     If *True*, legend marker is placed to the left of the legend label.
     If *False*, legend marker is placed to the right of the legend label.
 
+reverse : bool, default: False
+    If *True*, the legend labels are displayed in reverse order from the input.
+    If *False*, the legend labels are displayed in the same order as the input.
+
+    ..versionadded:: 3.7
+
 frameon : bool, default: :rc:`legend.frameon`
     Whether the legend should be drawn on a patch (frame).
 
@@ -312,6 +318,7 @@ def __init__(
         numpoints=None,      # number of points in the legend line
         markerscale=None,    # relative size of legend markers vs. original
         markerfirst=True,    # left/right ordering of legend marker and label
+        reverse=False,       # reverse ordering of legend marker and label
         scatterpoints=None,  # number of scatter points
         scatteryoffsets=None,
         prop=None,           # properties for the legend texts
@@ -437,6 +444,10 @@ def val_or_rc(val, rc_name):
                 _hand.append(handle)
         labels, handles = _lab, _hand
 
+        if reverse:
+            labels.reverse()
+            handles.reverse()
+
         handles = list(handles)
         if len(handles) < 2:
             ncols = 1
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -294,6 +294,38 @@ def test_legend_remove():
     assert ax.get_legend() is None
 
 
+def test_reverse_legend_handles_and_labels():
+    """Check that the legend handles and labels are reversed."""
+    fig, ax = plt.subplots()
+    x = 1
+    y = 1
+    labels = ["First label", "Second label", "Third label"]
+    markers = ['.', ',', 'o']
+
+    ax.plot(x, y, markers[0], label=labels[0])
+    ax.plot(x, y, markers[1], label=labels[1])
+    ax.plot(x, y, markers[2], label=labels[2])
+    leg = ax.legend(reverse=True)
+    actual_labels = [t.get_text() for t in leg.get_texts()]
+    actual_markers = [h.get_marker() for h in leg.legend_handles]
+    assert actual_labels == list(reversed(labels))
+    assert actual_markers == list(reversed(markers))
+
+
+@check_figures_equal(extensions=["png"])
+def test_reverse_legend_display(fig_test, fig_ref):
+    """Check that the rendered legend entries are reversed"""
+    ax = fig_test.subplots()
+    ax.plot([1], 'ro', label="first")
+    ax.plot([2], 'bx', label="second")
+    ax.legend(reverse=True)
+
+    ax = fig_ref.subplots()
+    ax.plot([2], 'bx', label="second")
+    ax.plot([1], 'ro', label="first")
+    ax.legend()
+
+
 class TestLegendFunction:
     # Tests the legend function on the Axes and pyplot.
     def test_legend_no_args(self):
