diff --git a/doc/index.rst b/doc/index.rst
index 66577ef0..eb619eac 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -1071,18 +1071,20 @@ Capsule objects
 Sentinel objects
 ~~~~~~~~~~~~~~~~
 
-.. class:: Sentinel(name, repr=None)
+.. class:: sentinel(name, /)
 
    A type used to define sentinel values. The *name* argument should be the
    name of the variable to which the return value shall be assigned.
 
-   If *repr* is provided, it will be used for the :meth:`~object.__repr__`
-   of the sentinel object. If not provided, ``"<name>"`` will be used.
+   A sentinel is bound to the module it is created within,
+   sentinels are not equal to similar named sentinels from other modules.
+
+   Assigning attributes to a sentinel including `__weakref__` is forbidden.
 
    Example::
 
-      >>> from typing_extensions import Sentinel, assert_type
-      >>> MISSING = Sentinel('MISSING')
+      >>> from typing_extensions import sentinel, assert_type
+      >>> MISSING = sentinel('MISSING')
       >>> def func(arg: int | MISSING = MISSING) -> None:
       ...     if arg is MISSING:
       ...         assert_type(arg, MISSING)
@@ -1091,6 +1093,13 @@ Sentinel objects
       ...
       >>> func(MISSING)
 
+   Sentinels defined inside a class scope should use a :term:`qualified name`.
+
+   Example::
+
+      >>> class MyClass:
+      ...     MISSING = sentinel('MyClass.MISSING')
+
    .. versionadded:: 4.14.0
 
       See :pep:`661`
diff --git a/src/test_typing_extensions.py b/src/test_typing_extensions.py
index f07e1eb0..bf25976a 100644
--- a/src/test_typing_extensions.py
+++ b/src/test_typing_extensions.py
@@ -102,6 +102,7 @@
     reveal_type,
     runtime,
     runtime_checkable,
+    sentinel,
     type_repr,
 )
 
@@ -9541,42 +9542,67 @@ def test_invalid_special_forms(self):
 
 
 class TestSentinels(BaseTestCase):
+    SENTINEL = sentinel("TestSentinels.SENTINEL")
+
     def test_sentinel_no_repr(self):
-        sentinel_no_repr = Sentinel('sentinel_no_repr')
+        sentinel_no_repr = sentinel('sentinel_no_repr')
 
-        self.assertEqual(sentinel_no_repr._name, 'sentinel_no_repr')
-        self.assertEqual(repr(sentinel_no_repr), '<sentinel_no_repr>')
+        self.assertEqual(sentinel_no_repr.__name__, 'sentinel_no_repr')
+        self.assertEqual(repr(sentinel_no_repr), 'sentinel_no_repr')
 
-    def test_sentinel_explicit_repr(self):
-        sentinel_explicit_repr = Sentinel('sentinel_explicit_repr', repr='explicit_repr')
+    def test_sentinel_deprecated_explicit_repr(self):
+        sentinel_explicit_repr = sentinel('sentinel_explicit_repr', repr='explicit_repr')
 
         self.assertEqual(repr(sentinel_explicit_repr), 'explicit_repr')
 
     @skipIf(sys.version_info < (3, 10), reason='New unions not available in 3.9')
     def test_sentinel_type_expression_union(self):
-        sentinel = Sentinel('sentinel')
+        sentinel_type = sentinel('sentinel')
 
-        def func1(a: int | sentinel = sentinel): pass
-        def func2(a: sentinel | int = sentinel): pass
+        def func1(a: int | sentinel_type = sentinel_type): pass
+        def func2(a: sentinel_type | int = sentinel_type): pass
 
-        self.assertEqual(func1.__annotations__['a'], Union[int, sentinel])
-        self.assertEqual(func2.__annotations__['a'], Union[sentinel, int])
+        self.assertEqual(func1.__annotations__['a'], Union[int, sentinel_type])
+        self.assertEqual(func2.__annotations__['a'], Union[sentinel_type, int])
 
     def test_sentinel_not_callable(self):
-        sentinel = Sentinel('sentinel')
+        sentinel_ = sentinel('sentinel')
         with self.assertRaisesRegex(
             TypeError,
-            "'Sentinel' object is not callable"
+            "'sentinel' object is not callable"
         ):
-            sentinel()
+            sentinel_()
+
+    def test_sentinel_copy_identity(self):
+        self.assertIs(self.SENTINEL, copy.copy(self.SENTINEL))
+        self.assertIs(self.SENTINEL, copy.deepcopy(self.SENTINEL))
+
+        anonymous_sentinel = sentinel("anonymous_sentinel")
+        self.assertIs(anonymous_sentinel, copy.copy(anonymous_sentinel))
+        self.assertIs(anonymous_sentinel, copy.deepcopy(anonymous_sentinel))
+
+    def test_sentinel_picklable_qualified(self):
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            self.assertIs(self.SENTINEL, pickle.loads(pickle.dumps(self.SENTINEL, protocol=proto)))
+
+    def test_sentinel_picklable_anonymous(self):
+        anonymous_sentinel = sentinel("anonymous_sentinel")  # Anonymous sentinel can not be pickled
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.assertRaisesRegex(
+                pickle.PicklingError,
+                r"attribute lookup anonymous_sentinel on \w+ failed|not found as \w+.anonymous_sentinel"
+            ):
+                self.assertIs(anonymous_sentinel, pickle.loads(pickle.dumps(anonymous_sentinel, protocol=proto)))
+
+    def test_sentinel_deprecated(self):
+        with self.assertWarnsRegex(DeprecationWarning, r"Subclassing sentinel is forbidden by PEP 661"):
+            class SentinelSubclass(Sentinel):
+                pass
+
+        my_sentinel = Sentinel(name="my_sentinel")
+        with self.assertWarnsRegex(DeprecationWarning, r"Setting attributes on sentinel is deprecated"):
+            my_sentinel.foo = "bar"
 
-    def test_sentinel_not_picklable(self):
-        sentinel = Sentinel('sentinel')
-        with self.assertRaisesRegex(
-            TypeError,
-            "Cannot pickle 'Sentinel' object"
-        ):
-            pickle.dumps(sentinel)
 
 def load_tests(loader, tests, pattern):
     import doctest
diff --git a/src/typing_extensions.py b/src/typing_extensions.py
index 20c331ee..b8bae93a 100644
--- a/src/typing_extensions.py
+++ b/src/typing_extensions.py
@@ -91,6 +91,7 @@
     'overload',
     'override',
     'Protocol',
+    'sentinel',
     'Sentinel',
     'reveal_type',
     'runtime',
@@ -159,22 +160,270 @@
 # Added with bpo-45166 to 3.10.1+ and some 3.9 versions
 _FORWARD_REF_HAS_CLASS = "__forward_is_class__" in typing.ForwardRef.__slots__
 
-class Sentinel:
+
+_overload_dummy = typing._overload_dummy
+
+if hasattr(typing, "get_overloads"):  # 3.11+
+    overload = typing.overload
+    get_overloads = typing.get_overloads
+    clear_overloads = typing.clear_overloads
+else:
+    # {module: {qualname: {firstlineno: func}}}
+    _overload_registry = collections.defaultdict(
+        functools.partial(collections.defaultdict, dict)
+    )
+
+    def overload(func):
+        """Decorator for overloaded functions/methods.
+
+        In a stub file, place two or more stub definitions for the same
+        function in a row, each decorated with @overload.  For example:
+
+        @overload
+        def utf8(value: None) -> None: ...
+        @overload
+        def utf8(value: bytes) -> bytes: ...
+        @overload
+        def utf8(value: str) -> bytes: ...
+
+        In a non-stub file (i.e. a regular .py file), do the same but
+        follow it with an implementation.  The implementation should *not*
+        be decorated with @overload.  For example:
+
+        @overload
+        def utf8(value: None) -> None: ...
+        @overload
+        def utf8(value: bytes) -> bytes: ...
+        @overload
+        def utf8(value: str) -> bytes: ...
+        def utf8(value):
+            # implementation goes here
+
+        The overloads for a function can be retrieved at runtime using the
+        get_overloads() function.
+        """
+        # classmethod and staticmethod
+        f = getattr(func, "__func__", func)
+        try:
+            _overload_registry[f.__module__][f.__qualname__][
+                f.__code__.co_firstlineno
+            ] = func
+        except AttributeError:
+            # Not a normal function; ignore.
+            pass
+        return _overload_dummy
+
+    def get_overloads(func):
+        """Return all defined overloads for *func* as a sequence."""
+        # classmethod and staticmethod
+        f = getattr(func, "__func__", func)
+        if f.__module__ not in _overload_registry:
+            return []
+        mod_dict = _overload_registry[f.__module__]
+        if f.__qualname__ not in mod_dict:
+            return []
+        return list(mod_dict[f.__qualname__].values())
+
+    def clear_overloads():
+        """Clear all overloads in the registry."""
+        _overload_registry.clear()
+
+
+# Python 3.13.8+ and 3.14.1+ contain a fix for the wrapped __init_subclass__
+# Breakpoint: https://github.com/python/cpython/pull/138210
+if ((3, 13, 8) <= sys.version_info < (3, 14)) or sys.version_info >= (3, 14, 1):
+    deprecated = warnings.deprecated
+else:
+    _T = typing.TypeVar("_T")
+
+    class deprecated:
+        """Indicate that a class, function or overload is deprecated.
+
+        When this decorator is applied to an object, the type checker
+        will generate a diagnostic on usage of the deprecated object.
+
+        Usage:
+
+            @deprecated("Use B instead")
+            class A:
+                pass
+
+            @deprecated("Use g instead")
+            def f():
+                pass
+
+            @overload
+            @deprecated("int support is deprecated")
+            def g(x: int) -> int: ...
+            @overload
+            def g(x: str) -> int: ...
+
+        The warning specified by *category* will be emitted at runtime
+        on use of deprecated objects. For functions, that happens on calls;
+        for classes, on instantiation and on creation of subclasses.
+        If the *category* is ``None``, no warning is emitted at runtime.
+        The *stacklevel* determines where the
+        warning is emitted. If it is ``1`` (the default), the warning
+        is emitted at the direct caller of the deprecated object; if it
+        is higher, it is emitted further up the stack.
+        Static type checker behavior is not affected by the *category*
+        and *stacklevel* arguments.
+
+        The deprecation message passed to the decorator is saved in the
+        ``__deprecated__`` attribute on the decorated object.
+        If applied to an overload, the decorator
+        must be after the ``@overload`` decorator for the attribute to
+        exist on the overload as returned by ``get_overloads()``.
+
+        See PEP 702 for details.
+
+        """
+        def __init__(
+            self,
+            message: str,
+            /,
+            *,
+            category: typing.Optional[typing.Type[Warning]] = DeprecationWarning,
+            stacklevel: int = 1,
+        ) -> None:
+            if not isinstance(message, str):
+                raise TypeError(
+                    "Expected an object of type str for 'message', not "
+                    f"{type(message).__name__!r}"
+                )
+            self.message = message
+            self.category = category
+            self.stacklevel = stacklevel
+
+        def __call__(self, arg: _T, /) -> _T:
+            # Make sure the inner functions created below don't
+            # retain a reference to self.
+            msg = self.message
+            category = self.category
+            stacklevel = self.stacklevel
+            if category is None:
+                arg.__deprecated__ = msg
+                return arg
+            elif isinstance(arg, type):
+                import functools
+                from types import MethodType
+
+                original_new = arg.__new__
+
+                @functools.wraps(original_new)
+                def __new__(cls, /, *args, **kwargs):
+                    if cls is arg:
+                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                    if original_new is not object.__new__:
+                        return original_new(cls, *args, **kwargs)
+                    # Mirrors a similar check in object.__new__.
+                    elif cls.__init__ is object.__init__ and (args or kwargs):
+                        raise TypeError(f"{cls.__name__}() takes no arguments")
+                    else:
+                        return original_new(cls)
+
+                arg.__new__ = staticmethod(__new__)
+
+                if "__init_subclass__" in arg.__dict__:
+                    # __init_subclass__ is directly present on the decorated class.
+                    # Synthesize a wrapper that calls this method directly.
+                    original_init_subclass = arg.__init_subclass__
+                    # We need slightly different behavior if __init_subclass__
+                    # is a bound method (likely if it was implemented in Python).
+                    # Otherwise, it likely means it's a builtin such as
+                    # object's implementation of __init_subclass__.
+                    if isinstance(original_init_subclass, MethodType):
+                        original_init_subclass = original_init_subclass.__func__
+
+                    @functools.wraps(original_init_subclass)
+                    def __init_subclass__(*args, **kwargs):
+                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                        return original_init_subclass(*args, **kwargs)
+                else:
+                    def __init_subclass__(cls, *args, **kwargs):
+                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                        return super(arg, cls).__init_subclass__(*args, **kwargs)
+
+                arg.__init_subclass__ = classmethod(__init_subclass__)
+
+                arg.__deprecated__ = __new__.__deprecated__ = msg
+                __init_subclass__.__deprecated__ = msg
+                return arg
+            elif callable(arg):
+                import asyncio.coroutines
+                import functools
+                import inspect
+
+                @functools.wraps(arg)
+                def wrapper(*args, **kwargs):
+                    warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                    return arg(*args, **kwargs)
+
+                if asyncio.coroutines.iscoroutinefunction(arg):
+                    # Breakpoint: https://github.com/python/cpython/pull/99247
+                    if sys.version_info >= (3, 12):
+                        wrapper = inspect.markcoroutinefunction(wrapper)
+                    else:
+                        wrapper._is_coroutine = asyncio.coroutines._is_coroutine
+
+                arg.__deprecated__ = wrapper.__deprecated__ = msg
+                return wrapper
+            else:
+                raise TypeError(
+                    "@deprecated decorator with non-None category must be applied to "
+                    f"a class or callable, not {arg!r}"
+                )
+
+
+def _caller(depth=1, default='__main__'):
+    try:
+        return sys._getframemodulename(depth + 1) or default
+    except AttributeError:  # For platforms without _getframemodulename()
+        pass
+    try:
+        return sys._getframe(depth + 1).f_globals.get('__name__', default)
+    except (AttributeError, ValueError):  # For platforms without _getframe()
+        pass
+    return None
+
+
+class sentinel:
     """Create a unique sentinel object.
 
     *name* should be the name of the variable to which the return value shall be assigned.
-
-    *repr*, if supplied, will be used for the repr of the sentinel object.
-    If not provided, "<name>" will be used.
     """
 
+    @overload
+    def __init__(self, name: str, /): ...
+
+    @overload
+    @deprecated("'name' must be positional-only, \
+'repr' is deprecated and must be removed.")
+    def __init__(self, name: str, repr: typing.Optional[str] = None): ...
+
     def __init__(
         self,
         name: str,
         repr: typing.Optional[str] = None,
     ):
-        self._name = name
-        self._repr = repr if repr is not None else f'<{name}>'
+        self.__name__ = name
+        self._repr = repr if repr is not None else name
+
+        # For pickling as a singleton:
+        self.__module__ = _caller()
+
+    @deprecated("Subclassing sentinel is forbidden by PEP 661")
+    def __init_subclass__(cls):
+        super().__init_subclass__()
+
+    def __setattr__(self, attr: str, value: object) -> None:
+        if attr not in {"__name__", "_repr", "__module__"}:
+            warnings.warn(
+                "Setting attributes on sentinel is deprecated",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+        super().__setattr__(attr, value)
 
     def __repr__(self):
         return self._repr
@@ -193,11 +442,14 @@ def __or__(self, other):
         def __ror__(self, other):
             return typing.Union[other, self]
 
-    def __getstate__(self):
-        raise TypeError(f"Cannot pickle {type(self).__name__!r} object")
+    def __reduce__(self) -> str:
+        """Reduce this sentinel to a singleton."""
+        return self.__name__  # Module is taken from the __module__ attribute
+
+Sentinel = sentinel
 
+_marker = sentinel("sentinel")
 
-_marker = Sentinel("sentinel")
 
 # The functions below are modified copies of typing internal helpers.
 # They are needed by _ProtocolMeta and they provide support for PEP 646.
@@ -458,75 +710,6 @@ def __getitem__(self, parameters):
                            instead of a type.""")
 
 
-_overload_dummy = typing._overload_dummy
-
-
-if hasattr(typing, "get_overloads"):  # 3.11+
-    overload = typing.overload
-    get_overloads = typing.get_overloads
-    clear_overloads = typing.clear_overloads
-else:
-    # {module: {qualname: {firstlineno: func}}}
-    _overload_registry = collections.defaultdict(
-        functools.partial(collections.defaultdict, dict)
-    )
-
-    def overload(func):
-        """Decorator for overloaded functions/methods.
-
-        In a stub file, place two or more stub definitions for the same
-        function in a row, each decorated with @overload.  For example:
-
-        @overload
-        def utf8(value: None) -> None: ...
-        @overload
-        def utf8(value: bytes) -> bytes: ...
-        @overload
-        def utf8(value: str) -> bytes: ...
-
-        In a non-stub file (i.e. a regular .py file), do the same but
-        follow it with an implementation.  The implementation should *not*
-        be decorated with @overload.  For example:
-
-        @overload
-        def utf8(value: None) -> None: ...
-        @overload
-        def utf8(value: bytes) -> bytes: ...
-        @overload
-        def utf8(value: str) -> bytes: ...
-        def utf8(value):
-            # implementation goes here
-
-        The overloads for a function can be retrieved at runtime using the
-        get_overloads() function.
-        """
-        # classmethod and staticmethod
-        f = getattr(func, "__func__", func)
-        try:
-            _overload_registry[f.__module__][f.__qualname__][
-                f.__code__.co_firstlineno
-            ] = func
-        except AttributeError:
-            # Not a normal function; ignore.
-            pass
-        return _overload_dummy
-
-    def get_overloads(func):
-        """Return all defined overloads for *func* as a sequence."""
-        # classmethod and staticmethod
-        f = getattr(func, "__func__", func)
-        if f.__module__ not in _overload_registry:
-            return []
-        mod_dict = _overload_registry[f.__module__]
-        if f.__qualname__ not in mod_dict:
-            return []
-        return list(mod_dict[f.__qualname__].values())
-
-    def clear_overloads():
-        """Clear all overloads in the registry."""
-        _overload_registry.clear()
-
-
 # This is not a real generic class.  Don't use outside annotations.
 Type = typing.Type
 
@@ -638,18 +821,6 @@ def _get_protocol_attrs(cls):
     return attrs
 
 
-def _caller(depth=1, default='__main__'):
-    try:
-        return sys._getframemodulename(depth + 1) or default
-    except AttributeError:  # For platforms without _getframemodulename()
-        pass
-    try:
-        return sys._getframe(depth + 1).f_globals.get('__name__', default)
-    except (AttributeError, ValueError):  # For platforms without _getframe()
-        pass
-    return None
-
-
 # `__match_args__` attribute was removed from protocol members in 3.13,
 # we want to backport this change to older Python versions.
 # Breakpoint: https://github.com/python/cpython/pull/110683
@@ -2907,151 +3078,6 @@ def method(self) -> None:
         return arg
 
 
-# Python 3.13.8+ and 3.14.1+ contain a fix for the wrapped __init_subclass__
-# Breakpoint: https://github.com/python/cpython/pull/138210
-if ((3, 13, 8) <= sys.version_info < (3, 14)) or sys.version_info >= (3, 14, 1):
-    deprecated = warnings.deprecated
-else:
-    _T = typing.TypeVar("_T")
-
-    class deprecated:
-        """Indicate that a class, function or overload is deprecated.
-
-        When this decorator is applied to an object, the type checker
-        will generate a diagnostic on usage of the deprecated object.
-
-        Usage:
-
-            @deprecated("Use B instead")
-            class A:
-                pass
-
-            @deprecated("Use g instead")
-            def f():
-                pass
-
-            @overload
-            @deprecated("int support is deprecated")
-            def g(x: int) -> int: ...
-            @overload
-            def g(x: str) -> int: ...
-
-        The warning specified by *category* will be emitted at runtime
-        on use of deprecated objects. For functions, that happens on calls;
-        for classes, on instantiation and on creation of subclasses.
-        If the *category* is ``None``, no warning is emitted at runtime.
-        The *stacklevel* determines where the
-        warning is emitted. If it is ``1`` (the default), the warning
-        is emitted at the direct caller of the deprecated object; if it
-        is higher, it is emitted further up the stack.
-        Static type checker behavior is not affected by the *category*
-        and *stacklevel* arguments.
-
-        The deprecation message passed to the decorator is saved in the
-        ``__deprecated__`` attribute on the decorated object.
-        If applied to an overload, the decorator
-        must be after the ``@overload`` decorator for the attribute to
-        exist on the overload as returned by ``get_overloads()``.
-
-        See PEP 702 for details.
-
-        """
-        def __init__(
-            self,
-            message: str,
-            /,
-            *,
-            category: typing.Optional[typing.Type[Warning]] = DeprecationWarning,
-            stacklevel: int = 1,
-        ) -> None:
-            if not isinstance(message, str):
-                raise TypeError(
-                    "Expected an object of type str for 'message', not "
-                    f"{type(message).__name__!r}"
-                )
-            self.message = message
-            self.category = category
-            self.stacklevel = stacklevel
-
-        def __call__(self, arg: _T, /) -> _T:
-            # Make sure the inner functions created below don't
-            # retain a reference to self.
-            msg = self.message
-            category = self.category
-            stacklevel = self.stacklevel
-            if category is None:
-                arg.__deprecated__ = msg
-                return arg
-            elif isinstance(arg, type):
-                import functools
-                from types import MethodType
-
-                original_new = arg.__new__
-
-                @functools.wraps(original_new)
-                def __new__(cls, /, *args, **kwargs):
-                    if cls is arg:
-                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
-                    if original_new is not object.__new__:
-                        return original_new(cls, *args, **kwargs)
-                    # Mirrors a similar check in object.__new__.
-                    elif cls.__init__ is object.__init__ and (args or kwargs):
-                        raise TypeError(f"{cls.__name__}() takes no arguments")
-                    else:
-                        return original_new(cls)
-
-                arg.__new__ = staticmethod(__new__)
-
-                if "__init_subclass__" in arg.__dict__:
-                    # __init_subclass__ is directly present on the decorated class.
-                    # Synthesize a wrapper that calls this method directly.
-                    original_init_subclass = arg.__init_subclass__
-                    # We need slightly different behavior if __init_subclass__
-                    # is a bound method (likely if it was implemented in Python).
-                    # Otherwise, it likely means it's a builtin such as
-                    # object's implementation of __init_subclass__.
-                    if isinstance(original_init_subclass, MethodType):
-                        original_init_subclass = original_init_subclass.__func__
-
-                    @functools.wraps(original_init_subclass)
-                    def __init_subclass__(*args, **kwargs):
-                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
-                        return original_init_subclass(*args, **kwargs)
-                else:
-                    def __init_subclass__(cls, *args, **kwargs):
-                        warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
-                        return super(arg, cls).__init_subclass__(*args, **kwargs)
-
-                arg.__init_subclass__ = classmethod(__init_subclass__)
-
-                arg.__deprecated__ = __new__.__deprecated__ = msg
-                __init_subclass__.__deprecated__ = msg
-                return arg
-            elif callable(arg):
-                import asyncio.coroutines
-                import functools
-                import inspect
-
-                @functools.wraps(arg)
-                def wrapper(*args, **kwargs):
-                    warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
-                    return arg(*args, **kwargs)
-
-                if asyncio.coroutines.iscoroutinefunction(arg):
-                    # Breakpoint: https://github.com/python/cpython/pull/99247
-                    if sys.version_info >= (3, 12):
-                        wrapper = inspect.markcoroutinefunction(wrapper)
-                    else:
-                        wrapper._is_coroutine = asyncio.coroutines._is_coroutine
-
-                arg.__deprecated__ = wrapper.__deprecated__ = msg
-                return wrapper
-            else:
-                raise TypeError(
-                    "@deprecated decorator with non-None category must be applied to "
-                    f"a class or callable, not {arg!r}"
-                )
-
 # Breakpoint: https://github.com/python/cpython/pull/23702
 if sys.version_info < (3, 10):
     def _is_param_expr(arg):