avoid hard dependency on typing_extensions

docs/reference/internal_modules.rst

@@ -25,6 +25,19 @@ Internal Modules
     :undoc-members:
     :show-inheritance:
 
+:mod:`~PIL._typing` Module
+--------------------------
+
+.. module:: PIL._typing
+
+Provides a convenient way to import type hints that are not available
+on some supported Python versions.
+
+.. py:data:: TypeGuard
+    :value: typing.TypeGuard
+
+    See :py:obj:`typing.TypeGuard`.
+
 :mod:`~PIL._util` Module
 ------------------------
 

pyproject.toml

@@ -37,9 +37,6 @@ classifiers = [
 dynamic = [
   "version",
 ]
-dependencies = [
-  'typing-extensions; python_version < "3.10"',
-]
 [project.optional-dependencies]
 docs = [
   "furo",
@@ -68,6 +65,9 @@ tests = [
   "pytest-cov",
   "pytest-timeout",
 ]
+typing = [
+  'typing-extensions; python_version < "3.10"',
+]
 xmp = [
   "defusedxml",
 ]

src/PIL/_typing.py

@@ -0,0 +1,16 @@
+import sys
+
+if sys.version_info >= (3, 10):
+    from typing import TypeGuard
+else:
+    try:
+        from typing_extensions import TypeGuard
+    except ImportError:
+        from typing import Any, Type
+
+        class TypeGuard:  # type: ignore[no-redef]
+            def __class_getitem__(cls, item: Any) -> Type[bool]:
+                return bool
+
+
+__all__ = ["TypeGuard"]

src/PIL/_util.py

@@ -1,14 +1,9 @@
 from __future__ import annotations
 
 import os
-import sys
 from pathlib import Path
 from typing import Any, NoReturn
-
-if sys.version_info >= (3, 10):
-    from typing import TypeGuard
-else:
-    from typing_extensions import TypeGuard
+from ._typing import TypeGuard
 
 
 def is_path(f: Any) -> TypeGuard[bytes | str | Path]:

tox.ini

@@ -37,3 +37,5 @@ deps =
     numpy
 commands =
     mypy src {posargs}
+extras =
+    typing