Add test, adapt example.

jmehne · Julian Mehne · commit d255e50e9822 · 2016-03-19T09:46:07.000+01:00
diff --git a/examples/pylab_examples/legend_demo6.py b/examples/pylab_examples/legend_demo6.py
@@ -1,22 +1,35 @@
+"""
+Showcases legend entries with more than one legend key.
+"""
 import matplotlib.pyplot as plt
 from matplotlib.legend_handler import HandlerTuple
 
 fig, (ax1, ax2) = plt.subplots(2, 1)
+
+# First plot: two legend keys for a single entry
 p1 = ax1.scatter([1], [5], c='r', marker='s', s=100)
 p2 = ax1.scatter([3], [2], c='b', marker='o', s=100)
+# `plot` returns a list, but we want the handle - thus the comma on the left
+p3, = ax1.plot([1, 5], [4, 4], 'm-d')
 
-l = ax1.legend([(p1, p2)], ['points'], scatterpoints=1,
-               handler_map={tuple: HandlerTuple(ndivide=0)})
+# Assign two of the handles to the same legend entry by putting them in a tuple
+# and using a generic handler map (which would be used for any additional
+# tuples of handles like (p1, p3)).
+l = ax1.legend([(p1, p3), p2], ['two keys', 'one key'], scatterpoints=1,
+               numpoints=1, handler_map={tuple: HandlerTuple(ndivide=0)})
 
-ind = [1, 2, 3]
-pos1 = [1, 3, 2]
-neg1 = [2, 1, 4]
-width = [0.5, 0.5, 0.5]
+# Second plot: plot two bar charts on top of each other and change the padding
+# between the legend keys
+x_left = [1, 2, 3]
+y_pos = [1, 3, 2]
+y_neg = [2, 1, 4]
 
-rpos1 = ax2.bar(ind, pos1, width=0.5, color='k', label='+1')
-rneg1 = ax2.bar(ind, neg1, width=0.5, color='w', hatch='///', label='-1')
+rneg = ax2.bar(x_left, y_neg, width=0.5, color='w', hatch='///', label='-1')
+rpos = ax2.bar(x_left, y_pos, width=0.5, color='k', label='+1')
 
-l = ax2.legend([(rpos1, rneg1)], ['Test'],
-               handler_map={(rpos1, rneg1): HandlerTuple(ndivide=0, pad=0.)})
+# Treat each legend entry differently by using specific `HandlerTuple`s
+l = ax2.legend([(rpos, rneg), (rneg, rpos)], ['pad!=0', 'pad=0'],
+               handler_map={(rpos, rneg): HandlerTuple(ndivide=0),
+                            (rneg, rpos): HandlerTuple(ndivide=0, pad=0.)})
 
 plt.show()
diff --git a/lib/matplotlib/tests/baseline_images/test_legend/legend_multiple_keys.png b/lib/matplotlib/tests/baseline_images/test_legend/legend_multiple_keys.png
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -18,6 +18,7 @@
 import matplotlib.patches as mpatches
 import matplotlib.transforms as mtrans
 
+from matplotlib.legend_handler import HandlerTuple
 
 @image_comparison(baseline_images=['legend_auto1'], remove_text=True)
 def test_legend_auto1():
@@ -77,6 +78,21 @@ def test_labels_first():
     ax.legend(loc=0, markerfirst=False)
 
 
+@image_comparison(baseline_images=['legend_multiple_keys'], extensions=['png'],
+                  remove_text=True)
+def test_multiple_keys():
+    # test legend entries with multiple keys
+    fig = plt.figure()
+    ax = fig.add_subplot(111)
+    p1, = ax.plot([1, 2, 3], '-o')
+    p2, = ax.plot([2, 3, 4], '-x')
+    p3, = ax.plot([3, 4, 5], '-d')
+    ax.legend([(p1, p2), (p2, p1), p3], ['two keys', 'pad=0', 'one key'],
+              numpoints=1,
+              handler_map={(p1, p2): HandlerTuple(ndivide=0),
+                           (p2, p1): HandlerTuple(ndivide=0, pad=0)})
+
+
 @image_comparison(baseline_images=['rgba_alpha'],
                   extensions=['png'], remove_text=True)
 def test_alpha_rgba():
