Backport PR #18079: Set shading='auto' if invalid value passed to pcolormesh

jklymak · meeseeksmachine · commit a0482853992d · 2020-07-27T14:33:10.000Z
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -5543,6 +5543,15 @@ def _pcolorargs(funcname, *args, shading='flat'):
         # - reset shading if shading='auto' to flat or nearest
         #   depending on size;
 
+        _valid_shading = ['gouraud', 'nearest', 'flat', 'auto']
+        try:
+            cbook._check_in_list(_valid_shading, shading=shading)
+        except ValueError as err:
+            cbook._warn_external(f"shading value '{shading}' not in list of "
+                                 f"valid values {_valid_shading}. Setting "
+                                 "shading='auto'.")
+            shading = 'auto'
+
         if len(args) == 1:
             C = np.asanyarray(args[0])
             nrows, ncols = C.shape
