Assigning attributes to typing.NoDefault raises TypeError, but should raise AttributeError

[AlexWaygood]

Bug report

Bug description:

Most sentinels in Python raise AttributeError if you try to assign attributes to them, but typing.NoDefault raises TypeError instead. I think this should be AttributeError, for consistency with other similar objects:

(main) % ./python.exe                                                                                                                ~/dev/cpython
Python 3.14.0a0 (heads/main:66f8bb76a1, May  8 2024, 17:00:15) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> None.foo = 'bar'
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    None.foo = 'bar'
    ^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'foo' and no __dict__ for setting new attributes
>>> NotImplemented.foo = 'bar'
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    NotImplemented.foo = 'bar'
    ^^^^^^^^^^^^^^^^^^
AttributeError: 'NotImplementedType' object has no attribute 'foo' and no __dict__ for setting new attributes
>>> from typing import NoDefault
>>> NoDefault.foo = 'bar'
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    NoDefault.foo = 'bar'
    ^^^^^^^^^^^^^
TypeError: 'NoDefaultType' object has no attributes (assign to .foo)

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-118895: Call PyType_Ready() on typing.NoDefault #118897
• [3.13] gh-118895: Call PyType_Ready() on typing.NoDefault (GH-118897) #118914