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()