python递归实现折半查找

1.Python 基础教程版：(有点没想清楚)

def search(sequence, number, lower=0, upper=None):
    if upper is None: upper = len(sequence) -1
    print 'sequence = ', sequence, 'number = ' , number,
          'lower = ', lower, 'upper = ', upper
    if lower == upper:
        assert number == sequence[upper]
        return upper
    else:
        middle = (lower + upper) // 2
        if number > sequence[middle]:
            return search(sequence, number, middle + 1, upper)
        else:
            return search(sequence, number, lower, middle)

2.自己实现版：

def search(sequence, number, lower=0, upper=None):
    if upper is None: upper = len(sequence) -1
    print 'sequence = ', sequence, 'number = ' , number,
          'lower = ', lower, 'upper = ', upper
    if lower > upper:
        #assert number == sequence[upper]
        print 'number is not in sequence'
        return -1
    else:
        middle = (lower + upper) // 2
        if number == sequence[middle]:
            return middle
        elif number > sequence[middle]:
            return search(sequence, number, middle + 1, upper)
        else:
            return search(sequence, number, lower, middle - 1)

def main():
    seq = [34, 67, 8, 123, 4, 100, 95, 175]
    seq.sort()
    print 'seq = ', seq
    n = input('please input a number from list:')
    print search(seq, n)

if __name__ == '__main__':
    main()