def human_seconds(interval):
    """Formats interval, a number of seconds, as a human-readable time
    interval using English words.
    """
    units = [
        (1, 'second'),
        (60, 'minute'),
        (60, 'hour'),
        (24, 'day'),
        (7, 'week'),
        (52, 'year'),
        (10, 'decade'),
    ]
    for i in range(len(units) - 1):
        increment, suffix = units[i]
        next_increment, _ = units[i + 1]
        interval /= float(increment)
        if interval < next_increment:
            break
    else:
        # Last unit.
        increment, suffix = units[-1]
        interval /= float(increment)

    return "%3.1f %ss" % (interval, suffix)