Stricter validation of rcParams["axes.axisbelow"].

anntzer · anntzer · commit 8bf19f2fd676 · 2020-02-29T09:38:55.000+01:00
I don't see a good reason to support "LiNefoobar" to mean "line", tbh...
diff --git a/doc/api/next_api_changes/deprecations.rst b/doc/api/next_api_changes/deprecations.rst
@@ -224,6 +224,12 @@ The following validators, defined in `.rcsetup`, are deprecated:
 value would be acceptable, one can test e.g. ``rc = RcParams(); rc[k] = v``
 raises an exception.
 
+Stricter rcParam validation
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+:rc:`axes.axisbelow` currently normalizes all strings starting with "line"
+(case-insensitive) to the option "line".  This is deprecated; in a future
+version only the exact string "line" (case-sensitive) will be supported.
+
 Toggling axes navigation from the keyboard using "a" and digit keys
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Axes navigation can still be toggled programmatically using
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -180,8 +180,14 @@ def validate_axisbelow(s):
         return validate_bool(s)
     except ValueError:
         if isinstance(s, str):
-            s = s.lower()
-            if s.startswith('line'):
+            if s == 'line':
+                return 'line'
+            if s.lower().startswith('line'):
+                cbook.warn_deprecated(
+                    "3.3", message=f"Support for setting axes.axisbelow to "
+                    f"{s!r} to mean 'line' is deprecated since %(since)s and "
+                    f"will be removed in %(removal)s; set it to 'line' "
+                    "instead.")
                 return 'line'
     raise ValueError('%s cannot be interpreted as'
                      ' True, False, or "line"' % s)
