Narrow RegexValidator.regex instance level type to Pattern[str]

django-stubs/core/validators.pyi

@@ -1,7 +1,7 @@
 from collections.abc import Callable, Collection, Sequence, Sized
 from decimal import Decimal
 from re import Pattern, RegexFlag
-from typing import Any, TypeAlias
+from typing import Any, Generic, TypeAlias, TypeVar, overload, type_check_only
 
 from django.core.files.base import File
 from django.utils.deconstruct import _Deconstructible
@@ -13,8 +13,19 @@ _Regex: TypeAlias = str | Pattern[str]
 
 _ValidatorCallable: TypeAlias = Callable[[Any], None]  # noqa: PYI047
 
+_ClassT = TypeVar("_ClassT")
+_InstanceT = TypeVar("_InstanceT")
+
+@type_check_only
+class ClassOrInstanceAttribute(Generic[_ClassT, _InstanceT]):
+    @overload
+    def __get__(self, obj: None, owner: type[object]) -> _ClassT: ...
+    @overload
+    def __get__(self, obj: object, owner: type[object]) -> _InstanceT: ...
+    def __set__(self, obj: object, value: _InstanceT) -> None: ...
+
 class RegexValidator(_Deconstructible):
-    regex: _Regex  # Pattern[str] on instance, but may be str on class definition
+    regex: ClassOrInstanceAttribute[_Regex, Pattern[str]]
     message: _StrOrPromise
     code: str
     inverse_match: bool

tests/assert_type/core/test_validators.py

@@ -0,0 +1,11 @@
+from re import Pattern
+from typing import assert_type
+
+from django.contrib.auth.validators import UnicodeUsernameValidator
+from django.core.validators import RegexValidator
+
+assert_type(RegexValidator.regex, str | Pattern[str])
+assert_type(RegexValidator().regex, Pattern[str])
+
+assert_type(UnicodeUsernameValidator.regex, str | Pattern[str])
+assert_type(UnicodeUsernameValidator().regex, Pattern[str])