The easiest solution would be to use SimpleQueue as suggested by user2357112's response - but I need to maintain support for python <3.7 which doesn't include it.

Upon further reading on python reentrancy, I learned signals can only trigger between atomic operations.

Therefore I switched from queue to deque, which is O(1) and atomic on both append() and popleft(), and therefore also thread-safe + signal-safe.

import signal
from collections import deque

event_queue = deque()

def signal_handler(signum, frame):
    event_queue.append(signum)
        
signal.signal(signal.SIGWINCH, signal_handler)

while True:
    if event_queue:
        evt = event_queue.popleft()
        print(f"Got an event: {evt}")