pywin32 cancelable message box

message_box.py

import msvcrt
import threading
import time
from typing import Callable, Set, Text

import win32con
import win32gui


def message_box(
    msg: Text,
    caption: Text,
    *,
    flags: int = 0,
    h_wnd: int = 0,
    on_close: Callable[[], None] = None,
) -> Callable[[], None]:
    def _run():
        win32gui.MessageBox(h_wnd, msg, caption, flags)
        if callable(on_close):
            on_close()
    t = threading.Thread(target=_run)
    t.start()
    h_wnd_set: Set[int] = set()

    def _iter_window(h_wnd, _):
        if win32gui.GetClassName(h_wnd) != "#32770": # message box
            return
        h_wnd_set.add(h_wnd)
    while not h_wnd_set:
        time.sleep(0.01)
        win32gui.EnumThreadWindows(t.ident, _iter_window, None)
    assert len(h_wnd_set) == 1, h_wnd_set

    def _close():
        for i in h_wnd_set:
            if win32gui.IsWindow(i):
                win32gui.PostMessage(i, win32con.WM_CLOSE, 0, 0)
        t.join()
    return _close


if __name__ == '__main__':
    close = message_box(
        "message", "caption",
        h_wnd=win32gui.FindWindow("CabinetWClass", None),
        on_close=lambda: print("close"),
    )
    print("Press any key")
    msvcrt.getch()
    close()