def circledDigits(num):
    """
    Converts a base-10 number into a string using unicode circled digits.
    That is, 123 becomes "①②③"
    """
    num = int(num)
    assert num >= 0
    digits = ["⓪", "①", "②", "③", "④", "⑤", "⑥", "⑦", "⑧", "⑨"]
    result = "".join(digits[int(d)] for d in str(num))
    return result