python-mss: Unjustified Screenshot error after closing a Tkinter Toplevel (Linux)

General information:

• OS name: Ubuntu Linux
• OS version: 22.04
• OS architecture: 64 bits
• Resolutions:
  • Monitor 1: 3440x1440 (issue occurs at all resolutions)
• Python version: 3.10.6
• MSS version: 6.1.0 & 7.0.1

For GNU/Linux users:

• Display server protocol and version, if known: X11 server
• Desktop Environment: ubuntu:GNOME
• Composite Window Manager name and version: X.Org v: 1.21.1.3, compositor: gnome-shell v: 42.5

Description of the warning/error

— The issue (and solution) is described in detail here —

In summary, the following error occurs when trying to instantiate an mss object after opening/closing a Tkinter Toplevel window. This error does not occur on Windows.

Full message

  File "/home/my_project/src/utilities/geometry.py", line 64, in screenshot
    with mss.mss() as sct:
  File "/home/my_project/env/lib/python3.10/site-packages/mss/factory.py", line 34, in mss
    return linux.MSS(**kwargs)
  File "/home/my_project/env/lib/python3.10/site-packages/mss/linux.py", line 297, in __init__
    self.root = self.xlib.XDefaultRootWindow(self._get_display(display))
  File "/home/my_project/env/lib/python3.10/site-packages/mss/linux.py", line 184, in validate
    raise ScreenShotError(f"{func.__name__}() failed", details=details)
mss.exception.ScreenShotError: XDefaultRootWindow() failed

Screenshot error: XDefaultRootWindow() failed, {'retval': <mss.linux.LP_XWindowAttributes object at 0x7f31d8d38ac0>, 
    'args': (<mss.linux.LP_Display object at 0x7f31d8d38740>,)}

Other details

The following code can be used to reproduce the error. Simply run this program and use the GUI button to open a new window that allows you to take a screenshot - then close the pop-up window and attempt to repeat the process.

import tkinter as tk

import mss
import mss.tools


def take_screenshot():
   with mss.mss() as sct:
       screen_part = {"top": 370, "left": 1090, "width": 80, "height": 390}
       sct_img = sct.grab(screen_part)
       mss.tools.to_png(sct_img.rgb, sct_img.size, output="./output.png")

def create_top_level_win():
   top_level_win = tk.Toplevel(root)

   take_screenshot_btn = tk.Button(top_level_win, text="Take screenshot", command=take_screenshot)
   take_screenshot_btn.pack()

root = tk.Tk()

btn = tk.Button(root, text="Open TopLevel", command=create_top_level_win)
btn.pack()

root.mainloop()

A temporary workaround is to reuse a single mss object throughout the application, like so:

sct = mss.mss()

def take_screenshot():
    global sct
    screen_part = {"top": 370, "left": 1090, "width": 80, "height": 390}
    sct_img = sct.grab(screen_part)
    mss.tools.to_png(sct_img.rgb, sct_img.size, output="./output.png")

On StackOverflow, one answer suggests that the bug is due to “the current implementation of MSS changing the current X11 error handler and leaving it afterwards, which causes a conflict with Tcl/Tk (the backend of Python Tkinter), see here for details”