Add validation for the orientation in stem().

QuLogic · QuLogic · commit 77d8cfb89832 · 2020-08-12T23:43:43.000-04:00
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2807,6 +2807,8 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None, bottom=0,
         if not 1 <= len(args) <= 5:
             raise TypeError('stem expected between 1 and 5 positional '
                             'arguments, got {}'.format(args))
+        cbook._check_in_list(['horizontal', 'vertical'],
+                             orientation=orientation)
 
         if len(args) == 1:
             y, = args
