Use the PEP 661 sentinel type where appropriate

pyproject.toml

@@ -30,7 +30,7 @@ requires-python = ">= 3.10"
 dependencies = [
     "exceptiongroup >= 1.0.2; python_version < '3.11'",
     "idna >= 2.8",
-    "typing_extensions >= 4.5; python_version < '3.13'",
+    "typing_extensions >= 4.16.0; python_version < '3.15'",
 ]
 dynamic = ["version"]
 

src/anyio/_backends/_trio.py

@@ -90,6 +90,9 @@
 if TYPE_CHECKING:
     from _typeshed import FileDescriptorLike
 
+if sys.version_info < (3, 15):
+    from typing_extensions import sentinel
+
 if sys.version_info >= (3, 11):
     from typing import TypeVarTuple, Unpack
 else:
@@ -195,7 +198,7 @@ def shield(self, value: bool) -> None:
 # Task groups
 #
 
-empty_start_value = object()
+empty_start_value = sentinel("empty_start_value")
 
 
 class _TrioTaskStatus(Generic[T_contra], abc.TaskStatus[T_contra]):

src/anyio/_core/_typedattr.py

@@ -1,13 +1,17 @@
 from __future__ import annotations
 
+import sys
 from collections.abc import Callable, Mapping
 from typing import Any, TypeVar, final, overload
 
 from ._exceptions import TypedAttributeLookupError
 
+if sys.version_info < (3, 15):
+    from typing_extensions import sentinel
+
 T_Attr = TypeVar("T_Attr")
 T_Default = TypeVar("T_Default")
-undefined = object()
+undefined = sentinel("undefined")
 
 
 def typed_attribute() -> Any:

src/anyio/itertools.py

@@ -42,9 +42,12 @@
 from ._core._tasks import CancelScope
 from .lowlevel import cancel_shielded_checkpoint, checkpoint, checkpoint_if_cancelled
 
+if sys.version_info < (3, 15):
+    from typing_extensions import sentinel
+
 T = TypeVar("T")
 R = TypeVar("R")
-_tee_end = object()
+_tee_end = sentinel("_tee_end")
 
 
 @dataclass(eq=False)