Timed input in python 3 for Mac and Windows

I need a timed input for python 3 on both Mac and Windows which, if the user runs out of time, automatically chooses one of the options. Every other answer for a question I've seen only terminates after user presses 'Enter'. I need it to terminate regardless of any 'Enter' pressed or not.

For example, in my chess program, if no input is given after 5 seconds, I need it to automatically choose "Q". Also if the input is not in ["Q", "R", "B", "N"] then I also need it to choose "Q".

The following code doesn't work. It'll ask for the input then wait forever; the timer doesn't work at all.

def countdown():
    global timer
    timer = 5
    for x in range(timer):
        timer -= 1
        time.sleep(1)

countdownThread = threading.Thread(target=countdown)
countdownThread.start()

while timer > 0:
    promotedPiece = input("Promote to Q, R, B or N? >  ").upper()
    if timer == 0:
        break

if timer == 0:
    if promotedPiece not in ["Q", "R", "B", "N"]:  # If not valid input, choose Queen
        promotedPiece = "Q"
        print("Queen auto selected")

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