def scale_to_one(iterable):
    """
    Scale an iterable of numbers proportionally such as the highest number
    equals to 1

    Example:
        >> > scale_to_one([5, 4, 3, 2, 1])
        [1, 0.8, 0.6, 0.4, 0.2]
    """
    m = max(iterable)
    return [v / m for v in iterable]