ctypes: constructor of _FuncPointer can accept None to paramflags and Structure to iid in runtime

[AmberAnsari89]

fixes #8968

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

comtypes (https://github.com/enthought/comtypes)
- comtypes/_memberspec.py:357: error: No overload variant of "_FuncPointer" matches argument types "int", "str", "None", "Optional[GUID]"  [call-overload]
- comtypes/_memberspec.py:357: note: Possible overload variants:
- comtypes/_memberspec.py:357: note:     def __init__(self, address: int) -> _FuncPointer
- comtypes/_memberspec.py:357: note:     def __init__(self, callable: Callable[..., Any]) -> _FuncPointer
- comtypes/_memberspec.py:357: note:     def __init__(self, func_spec: Tuple[Union[str, int], CDLL], paramflags: Tuple[Union[Tuple[int], Tuple[int, str], Tuple[int, str, Any]], ...] = ...) -> _FuncPointer
- comtypes/_memberspec.py:357: note:     def __init__(self, vtlb_index: int, name: str, paramflags: Tuple[Union[Tuple[int], Tuple[int, str], Tuple[int, str, Any]], ...] = ..., iid: _Pointer[c_int] = ...) -> _FuncPointer
- comtypes/_memberspec.py:358: error: No overload variant of "_FuncPointer" matches argument types "int", "str", "Optional[Tuple[Union[Tuple[int, Optional[str]], Tuple[int, Optional[str], Any]], ...]]", "Optional[GUID]"  [call-overload]
- comtypes/_memberspec.py:358: note: Possible overload variants:
- comtypes/_memberspec.py:358: note:     def __init__(self, address: int) -> _FuncPointer
- comtypes/_memberspec.py:358: note:     def __init__(self, callable: Callable[..., Any]) -> _FuncPointer
- comtypes/_memberspec.py:358: note:     def __init__(self, func_spec: Tuple[Union[str, int], CDLL], paramflags: Tuple[Union[Tuple[int], Tuple[int, str], Tuple[int, str, Any]], ...] = ...) -> _FuncPointer
- comtypes/_memberspec.py:358: note:     def __init__(self, vtlb_index: int, name: str, paramflags: Tuple[Union[Tuple[int], Tuple[int, str], Tuple[int, str, Any]], ...] = ..., iid: _Pointer[c_int] = ...) -> _FuncPointer

[JelleZijlstra]

Let's leave this change for another PR.

[JelleZijlstra]

The ctypes code can be hard to follow, but I think there's more we can do here to improve things. The implementation of the code being changed here is at https://github.com/python/cpython/blob/8f18ac04d32515eab841172c956a8cb14bcee9c3/Modules/_ctypes/_ctypes.c#L3627.

• Our stub has a _FuncPointer class that doesn't exist at runtime. But in fact, the code returns a subclass of _ctypes.CFuncPtr, so why don't we use that class in the stubs?
• All of the arguments are positional-only and should be marked as such in the stub.
• We're missing an overload for the case where no arguments are passed to the constructor.
• The overload with vtbl_index (not vtlb_index as the stub calls it) should exist only on Windows.

[AmberAnsari89]

thank you @JelleZijlstra for these information. However, i did not understand much from these.
Can you please guide me a bit more to understand with reference to actual requirement of issue under -- The constructor of _FuncPointer can accept None to paramflags and Structure to iid in runtime. #8968