MNT: Deprecate other capitalization than "None" in matplotlibrc

rcomer · timhoffm · commit 61a0829b7340 · 2025-01-27T15:58:45.000+01:00
The `*_or_None` validators have accepted any capitalization of the string "none" as input. This is overly permissive and will likely lead to conflicts in the future because we cannot distinguish between resolving to `None` and `"none"` which may be need for some parameters in the future. Inspired by #29481.
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -191,6 +191,13 @@ def _make_type_validator(cls, *, allow_none=False):
     def validator(s):
         if (allow_none and
                 (s is None or cbook._str_lower_equal(s, "none"))):
+            if cbook._str_lower_equal(s, "none") and s != "None":
+                _api.warn_deprecated(
+                    "3.11",
+                    message=f"Using the capitalization {s!r} in matplotlibrc for "
+                            "*None* is deprecated in %(removal)s and will leaa to "
+                            "an error two versions later. Please use 'None' instead."
+                )
             return None
         if cls is str and not isinstance(s, str):
             raise ValueError(f'Could not convert {s!r} to str')
