Consistent handling fo *args in Axes.stem

Zac-HD · Zac-HD · commit adf3784be11d · 2018-05-19T00:08:49.000+10:00
diff --git a/doc/api/next_api_changes/2018-05-06-ZHD.rst b/doc/api/next_api_changes/2018-05-06-ZHD.rst
@@ -0,0 +1,7 @@
+Consistent handling of *args in Axes.stem
+-----------------------------------------
+
+:meth:`matplotlib.axex.Axes.stem` now raises TypeError when passed
+unhandled positional arguments.  If two or more arguments are passed
+(ie X, Y, [linefmt], ...) and Y cannot be cast to an array, an error\
+will be raised instead of treating X as Y and Y as linefmt.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -2350,18 +2350,20 @@ def stem(self, *args, linefmt=None, markerfmt=None, basefmt=None,
             which inspired this method.
 
         """
+        if len(args) > 5:
+            raise TypeError('Too many positional arguments')
+
         # Assume there's at least one data array
         y = np.asarray(args[0])
         args = args[1:]
 
         # Try a second one
         try:
-            x, y = y, np.asarray(args[0], dtype=float)
-        except (IndexError, ValueError):
-            # The second array doesn't make sense, or it doesn't exist
+            x, *args = args
+        except IndexError:
             x = np.arange(len(y))
         else:
-            args = args[1:]
+            x, y = y, np.asarray(x, dtype=float)
 
         # defaults for formats
         if linefmt is None:
