def progress_bar(done, total, length=10, bar='#', sep='-'):
    """
    Return a string indicating graphically the percentage of the first argument
    to the second

    >>> progress_bar(3, 6)
    "#####-----"
    """
    fraction = float(done) / total
    bars = int(fraction * length)
    return '{}{}'.format(str(bar) * bars, str(sep) * (length - bars))
