[Python] win32gui - Unable to SendMessage unless window is focused

Hi I'm trying to create a simple script that types the letter A into a window.

In this case, the window is Old School Runescape. Yes it is a game.

Here's the little code I use.

import win32gui, win32ui, win32con, win32api
import time

if __name__ == "__main__":
window_name = "Old School RuneScape"
hwnd = win32gui.FindWindow(None, window_name)

win = win32ui.CreateWindowFromHandle(hwnd)

while True:
print("Sending")
win.SendMessage(win32con.WM_CHAR, ord('A'), 0)
time.sleep(2)


This code works on various other programs. However, particularly for this, it doesn't work unless the game window is in focus.

I suspected that there might be an inner window as this is a game, so I did a little check and found that there's an inner window.:

{'SunAwtCanvas': 1771602}


But, it still doesn't work when I try to send to the Main / Inner window.

I followed the documentation on Microsoft's site as well as researched quite a bit on Stackoverflow for some help but to no avail.

Does anyone know what might be the issue?

Update 1
I tried using

win.PostMessage(win32con.WM_CHAR, 0x44, 0)


Still, it only works when the window is focused.

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