def get_fraction(number: int) -> float:
    """
    Return the fraction associated with a fractional part.

        >>> get_fraction(9)
        0.9
        >>> get_fraction(123)
        0.123
        >>> get_fraction(1)
        0.1

    """
    if number < 0:
        raise Exception("Number should be a positive integer")

    # we could do this analytically, but there are too many edge
    # cases (0 and 10^n, eg)
    result = float(number)
    while result >= 1:
        result /= 10

    return result