...Fix warnings.warn->cbook._warn_external

jklymak · web-flow · commit be0dc01a3e42 · 2019-01-04T09:38:49.000-08:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2638,7 +2638,7 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None, bottom=0,
             self.add_collection(stemlines)
         # Old behaviour is to plot each of the lines individually
         else:
-            warnings.warn(
+            cbook._warn_extrnal(
                 'In Matplotlib 3.3 individual lines on a stem plot will be '
                 'added as a LineCollection instead of individual lines.\n'
                 'This significantly improves the performance of a stem plot.\n'
