Improve error for quoted values in matplotlibrc.

anntzer · anntzer · commit 14a30f640582 · 2020-03-30T15:05:45.000+02:00
... as the need for unquoted values in the matplotlibrc is slightly
confusing.

Also reword the error message to match the one in
_check_in_list/_check_getitem.
diff --git a/lib/matplotlib/rcsetup.py b/lib/matplotlib/rcsetup.py
@@ -72,8 +72,13 @@ def __call__(self, s):
             s = s.lower()
         if s in self.valid:
             return self.valid[s]
-        raise ValueError('Unrecognized %s string %r: valid strings are %s'
-                         % (self.key, s, list(self.valid.values())))
+        msg = (f"{s!r} is not a valid value for {self.key}; supported values "
+               f"are {[*self.valid.values()]}")
+        if ((s.startswith('"') and s.endswith('"')
+             or s.startswith("'") and s.endswith("'"))
+                and s[1:-1] in self.valid):
+            msg += f"; remove quotes surrounding your string"
+        raise ValueError(msg)
 
 
 def _listify_validator(scalar_validator, allow_stringlist=False, *, doc=None):
