[quietbritishjim]

Nitpick: you could replace sys.stdout.write(f"{n}\n") with print(n). The current code looks very much like it was written for Python 2 (apart from the f string!), where print was a statement. As of Python 3, print is just a regular function. It returns None, which is falsey, so you'd also need to change your first "and" to an "or".

[jftuga]

Thanks for this suggestion - it works great.

    import sys # run: python3 countdown.py 10
    def main(n:int): print(n) or n-1 and main(n-1)
    main(int(sys.argv[1]))

This also works and is definitely more Pythonic:

    _ = [print(n) for n in range(10,0,-1)]