Using pywin32 win32gui.IsWindow to check if a Window still exists

win32gui_iswindow.py

'''Using pywin32 to check if a Window still exists.

Requirements:
- pywin32

Problem:
I am presented with a custom Excel XLAM ribbon which has a password-protected backend code.
This ribbon has the functionality to bring out a message box and/or UserForm.
You want Python to execute some functions soon as these message boxes and/or UserForm close.

Resources:
The existing code already make use of `win32gui.EnumWindows`.

Solution:
1. Check if message boxes/UserForm have their own hwnd. They have.
2. Check if it is possible to know whether or not certain hwnd still exists.
Turns out `IsWindow()` is part of Windows API and is available as `win32gui.IsWindow`.

To simulate the code below, have Excel create a sample
message box using the code below:

    ```vba
    Sub main()
        MsgBox "Hello World", Title:="FIND ME"
    End Sub
    ```

Do NOT press OK. Run the Python script.

Further improvements:
Do take note that Windows can reuse hwnd.
It is worth exploring if it is possible to
integrate the code in asynchronous processes.'''

from time import sleep
import win32gui

MSGBOX_TITLE = 'FIND ME'
CHECK_INTERVAL = 0.5

def callback(hwnd, custom_list):
    custom_list.append((hwnd, win32gui.GetWindowText(hwnd)))

def check_exists(hwnd):
    try:
        exists = True
        while exists:
            if win32gui.IsWindow(hwnd):
                print('Exists...')
                sleep(CHECK_INTERVAL)
            else:
                exists = False
    except KeyboardInterrupt:
        raise SystemExit

if __name__ == '__main__':
    win32gui.EnumWindows(callback, windows := [])
    for handle, title in windows:
        if title == MSGBOX_TITLE:
            hwnd_target = handle
            check_exists(hwnd_target)