Wrap python-xlib's Xlib.display.next_event() so it does not block the main loop

xlib-non-blocking-event-loop.py

""" 
python-xlib's Xlib.display.next_event() does not have a timeout when waiting for an event to be queued.
It may block the script's execution forever.

Workaround:
Call display.next_event() only if an event is available in the queue.
Use select.select() on the xserver's socket to wait for an event and specify a timeout.

based on: https://stackoverflow.com/a/8592969/5894777

python-xlib: https://github.com/python-xlib/python-xlib

tags: x11, xorg, x.org, xwindow-system, xlib, python-xlib, event queue, XNextEvent, wait, non-blocking, timeout
"""

import select
import Xlib.display

def x_wait_for_event(xdisplay, timeout_seconds):
    """ Wait up to `timeout_seconds` seconds for an event to be queued.
        Return True, if a xevent is available.
        Return False, if the timeout was reached. """
    rlist = select.select(
        [xdisplay.display.socket], # rlist
        [], # wlist
        [], # xlist
        timeout_seconds, # timeout [seconds]
    )[0]
    return len(rlist) > 0
  
def handle_xevent(event):

 
xdisplay = Xlib.display.Display()

# setup x client etc.
# ...

# main loop:
while True:
    while xdisplay.pending_events():
        print(xdisplay.next_event())
    if not x_wait_for_event(xdisplay, timeout_seconds=1):
        print('timeout')
    # check other sources for events...