Fix stem(use_line_collection)

timhoffm · timhoffm · commit 013dfc1ee58d · 2019-03-24T01:44:06.000+01:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2779,8 +2779,9 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None, bottom=0,
 
         # New behaviour in 3.1 is to use a LineCollection for the stemlines
         if use_line_collection:
-            stemlines = []
             stemlines = [((xi, bottom), (xi, yi)) for xi, yi in zip(x, y)]
+            if linestyle is None:
+                linestyle = rcParams['lines.linestyle']
             stemlines = mcoll.LineCollection(stemlines, linestyles=linestyle,
                                              colors=linecolor,
                                              label='_nolegend_')
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -3070,6 +3070,19 @@ def test_stem(use_line_collection):
     ax.legend()
 
 
+@check_figures_equal(extensions=['png'])
+def test_stem_params(fig_test, fig_ref):
+    x = np.linspace(0, 3.14, 37)
+    y = np.sin(x)
+
+    ax = fig_test.subplots()
+    ax.stem(x, y, linefmt='grey', use_line_collection=True)
+
+    ax = fig_ref.subplots()
+    with pytest.warns(UserWarning):
+        ax.stem(x, y, linefmt='grey')
+
+
 def test_stem_args():
     fig = plt.figure()
     ax = fig.add_subplot(1, 1, 1)
