isinstance(..., Optional[Any]) always returns False

[jcal-15]

Bug report

Bug description:

isinstance(..., Optional[Any]) is always returning False. Based off of behavior of other types I am pretty sure that isinstance should raise a TypeError

# Add a code block here, if required
>>> from typing import Optional, Any

# ✅ `Any` raises a TypeError
>>> isinstance(1, Any)
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    isinstance(1, Any)
    ~~~~~~~~~~^^^^^^^^
  File "C:\Program Files\Python313\Lib\typing.py", line 589, in __instancecheck__
    raise TypeError("typing.Any cannot be used with isinstance()")
TypeError: typing.Any cannot be used with isinstance()

# ✅ Generic types raise type errors
>>> isinstance(1, list[int])
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    isinstance(1, list[int])
    ~~~~~~~~~~^^^^^^^^^^^^^^
TypeError: isinstance() argument 2 cannot be a parameterized generic

# ✅ Optional of Generic types raise type errors
>>> isinstance(1, Optional[list[int]])
Traceback (most recent call last):
  File "<python-input-10>", line 1, in <module>
    isinstance(1, Optional[list[int]])
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Python313\Lib\typing.py", line 1786, in __instancecheck__
    return self.__subclasscheck__(type(obj))
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "C:\Program Files\Python313\Lib\typing.py", line 1790, in __subclasscheck__
    if issubclass(cls, arg):
       ~~~~~~~~~~^^^^^^^^^^
TypeError: issubclass() argument 2 cannot be a parameterized generic
>>>

# ❌ Optional of `Any` returns false
>>> isinstance(1, Optional[Any])
False
>>> isinstance(Any, Optional[Any])
False
>>> isinstance("Any", Optional[Any])
False
>>>

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

Windows

[JelleZijlstra]

This appears to be because Optional[Any] produces a typing.Union, and its __instancecheck__ is implemented by delegating to __subclasscheck__, and somehow you can do issubclass() on Any:

>>> issubclass(int, Any)
False

[serhiy-storchaka]

This looks related to #88834 (or the same issue).

[serhiy-storchaka]

Closing as a duplicate of #88834.