Retry Until Valid

The ask-again loop

Crashing on the first bad keystroke is not acceptable in real software, and silently accepting garbage is worse. The standard fix combines three tools you already own: while True: from lesson 5-2, try/except from lesson 9-2, and break. Attempt the conversion, and only break out of the loop once it succeeds:

while True:
    raw = input()
    try:
        n = int(raw)
        break
    except ValueError:
        print("not a number, try again")

The break sits inside the try, on the line after the conversion, because that placement encodes the logic: reaching the break proves int(raw) did not raise, so the loop only ends on success. Every command-line tool that asks for a number, a date, or a menu choice runs a loop of exactly this shape.