Harmonize error messages from _api.check_in_list and _api.getitem_checked

QuLogic · QuLogic · commit 6cdfe15687d1 · 2026-04-17T13:59:44.000-04:00
This also means that the former now gains suggestions.
diff --git a/lib/matplotlib/_api/__init__.py b/lib/matplotlib/_api/__init__.py
@@ -107,6 +107,36 @@ def type_name(tp):
                     type_name(type(v))))
 
 
+def list_suggestion_error_msg(name, potential, values):
+    """
+    Generate an error message if a potential setting is not an acceptable value.
+
+    If the acceptable values are all strings, and sufficiently large, then add just a
+    few suggestions to the end of the message. Otherwise list the supported values.
+
+    Parameters
+    ----------
+    name : str
+        The name of the setting, keyword argument, etc. to generate the message for.
+    potential
+        The potential value from the user that is not a valid choice.
+    values : iterable
+        Sequence of values to check on.
+    """
+    if len(values) > 5 and all(isinstance(v, str) for v in [potential, *values]):
+        best = difflib.get_close_matches(potential, values, cutoff=0.5)
+        match len(best):
+            case 0:
+                suggestion = ""
+            case 1:
+                suggestion = f" Did you mean: {best[0]!r}?"
+            case _:
+                suggestion = f" Did you mean one of: {', '.join(map(repr, best))}?"
+    else:
+        suggestion = f" Supported values are {', '.join(map(repr, values))}"
+    return f"{potential!r} is not a valid value for {name}.{suggestion}"
+
+
 def check_in_list(values, /, **kwargs):
     """
     For each *key, value* pair in *kwargs*, check that *value* is in *values*;
@@ -146,9 +176,7 @@ def check_in_list(values, /, **kwargs):
             # the individual `val == values[i]` ValueError surface.
             exists = False
         if not exists:
-            msg = (f"{val!r} is not a valid value for {key}"
-                   f"; supported values are {', '.join(map(repr, values))}")
-            raise ValueError(msg)
+            raise ValueError(list_suggestion_error_msg(key, val, values))
 
 
 def check_shape(shape, /, **kwargs):
@@ -207,18 +235,7 @@ def getitem_checked(mapping, /, _error_cls=ValueError, **kwargs):
     try:
         return mapping[v]
     except KeyError:
-        if len(mapping) > 5:
-            best = difflib.get_close_matches(v, mapping.keys(), cutoff=0.5)
-            match len(best):
-                case 0:
-                    suggestion = ""
-                case 1:
-                    suggestion = f" Did you mean: {best[0]!r}?"
-                case _:
-                    suggestion = f" Did you mean one of: {', '.join(map(repr, best))}?"
-        else:
-            suggestion = f" Supported values are {', '.join(map(repr, mapping))}"
-        raise _error_cls(f"{v!r} is not a valid value for {k}.{suggestion}") from None
+        raise _error_cls(list_suggestion_error_msg(k, v, mapping.keys())) from None
 
 
 def caching_module_getattr(cls):
diff --git a/lib/matplotlib/_api/__init__.pyi b/lib/matplotlib/_api/__init__.pyi
@@ -38,6 +38,7 @@ class classproperty(Any):
 def check_isinstance(
     types: type | tuple[type | None, ...], /, **kwargs: Any
 ) -> None: ...
+def list_suggestion_error_msg(name: str, potential: str, values: Sequence[Any]) -> str: ...
 def check_in_list(values: Sequence[Any], /, **kwargs: Any) -> None: ...
 def check_shape(shape: tuple[int | None, ...], /, **kwargs: NDArray) -> None: ...
 def getitem_checked(
diff --git a/lib/matplotlib/tests/test_transforms.py b/lib/matplotlib/tests/test_transforms.py
@@ -1072,8 +1072,8 @@ def test_scale_swapping(fig_test, fig_ref):
 
 def test_offset_copy_errors():
     with pytest.raises(ValueError,
-                       match="'fontsize' is not a valid value for units;"
-                             " supported values are 'dots', 'points', 'inches'"):
+                       match="'fontsize' is not a valid value for units. "
+                             "Supported values are 'dots', 'points', 'inches'"):
         mtransforms.offset_copy(None, units='fontsize')
 
     with pytest.raises(ValueError,
