xseticon.py - Set X11 window icon using ctypes and PIL (no extra deps)

xseticon.py

#!/usr/bin/env python3
"""Set X11 window icon from a PNG file using ctypes (no dependencies beyond PIL).

https://gist.github.com/gatopeich/9d0c61cae0a4e01b23b0afc543c27fbb
Author: gatopeich @ github
"""
import ctypes
import ctypes.util
import sys
from PIL import Image

def set_icon(window_id, icon_path):
    x11 = ctypes.cdll.LoadLibrary(ctypes.util.find_library("X11"))
    display = x11.XOpenDisplay(None)
    if not display:
        sys.exit("Cannot open display")

    img = Image.open(icon_path).convert("RGBA")
    w, h = img.size
    data = [w, h]
    for r, g, b, a in zip(*[iter(img.tobytes())] * 4):
        data.append((a << 24) | (r << 16) | (g << 8) | b)

    atom = x11.XInternAtom(display, b"_NET_WM_ICON", False)
    cardinal = x11.XInternAtom(display, b"CARDINAL", False)
    arr = (ctypes.c_ulong * len(data))(*data)

    x11.XChangeProperty(
        display, window_id, atom, cardinal, 32,
        0,  # PropModeReplace
        ctypes.cast(arr, ctypes.POINTER(ctypes.c_ubyte)),
        len(data),
    )
    x11.XFlush(display)
    x11.XCloseDisplay(display)

if __name__ == "__main__":
    if len(sys.argv) != 3:
        sys.exit(f"Usage: {sys.argv[0]} <window_id> <icon.png>")
    set_icon(int(sys.argv[1]), sys.argv[2])