python递归实现折半查找

1.Python 基础教程版：(有点没想清楚)

 1 def search(sequence, number, lower=0, upper=None):
 2     if upper is None: upper = len(sequence) -1
 3     print 'sequence = ', sequence, 'number = ' , number,
 4           'lower = ', lower, 'upper = ', upper
 5     if lower == upper:
 6         assert number == sequence[upper]
 7         return upper
 8     else:
 9         middle = (lower + upper) // 2
10         if number > sequence[middle]:
11             return search(sequence, number, middle + 1, upper)
12         else:
13             return search(sequence, number, lower, middle)

2.自己实现版：

 1 def search(sequence, number, lower=0, upper=None):
 2     if upper is None: upper = len(sequence) -1
 3     print 'sequence = ', sequence, 'number = ' , number,
 4           'lower = ', lower, 'upper = ', upper
 5     if lower > upper:
 6         #assert number == sequence[upper]
 7         print 'number is not in sequence'
 8         return -1
 9     else:
10         middle = (lower + upper) // 2
11         if number == sequence[middle]:
12             return middle
13         elif number > sequence[middle]:
14             return search(sequence, number, middle + 1, upper)
15         else:
16             return search(sequence, number, lower, middle - 1)
17 
18 def main():
19     seq = [34, 67, 8, 123, 4, 100, 95, 175]
20     seq.sort()
21     print 'seq = ', seq
22     n = input('please input a number from list:')
23     print search(seq, n)
24 
25 if __name__ == '__main__':
26     main()