Ludicrous partition function

partition.py

def partition_will(pred, values):
    if not values:
        return [], []
    if len(values) == 1:
        return ([], values) if pred(values[0]) else (values, [])
    values = sorted(values, key=pred)
    lower = 0
    upper = len(values)
    index = (lower + upper) // 2
    try:
        while index:
            value = pred(values[index])
            if pred(values[index + 1]) and not value:
                index += 1
                return values[:index], values[index:]
            if value:
                upper = index
            else:
                lower = index
            index = (lower + upper) // 2

    except IndexError:
        return values[:], []
    return [], values[:]