hidden screenshot with xlib and PIL

screenshot.py

#!/usr/bin/env python
import os
from Xlib import display, X
from PIL import Image 

dsp = display.Display()
screen = dsp.screen()
W = screen.width_in_pixels
H = screen.height_in_pixels

root = screen.root
raw = root.get_image(0, 0, W, H, X.ZPixmap, 0xffffffff)
image = Image.frombytes("RGB", (W, H), raw.data, "raw", "BGRX")

file_path = os.path.join(os.environ['HOME'], '.screenshot.png')
image.save(file_path)

you can simply get resolution of screen by dsp.screen().width_in_pixels, dsp.screen().height_in_pixels

That's right, thanks!
Updating to be more concise using your suggestion.