二分算法

 1 def binary_search(sorted_sequence, item):
 2     """
 3     sorted_sequence: 有序序列
 4     item: 需要查找的元素值
 5     return: 若序列中存在该元素，则返回该元素索引，若不存在，则返回None
 6     """
 7      low = 0
 8      high = len(sorted_sequence) - 1
 9      while low <= high:
10          mid = (low + high) // 2
11          guess = sorted_sequence[mid]
12          if guess == item:
13              return mid
14          if guess > item:
15              high = mid - 1
16          else:
17              low = mid + 1
18      return None